Algorithms and Data structures

• aho_corasick - AhoCorasick algorithm
• crystal-diff - A Crystal sequence differencing implementation
• crystaledge - A pure Vector Math library
• crystalline - A collection of containers and algorithms
• delimiter_tree - A tree structure that is built using a delimiter
• edits.cr - Collection of edit distance algorithms
• markov - Build Markov Chains and run Markov Processes
• miller_rabin - Implements Miller-Rabin algorithm to check if a number is prime
• multiset.cr - Implementation of a multiset
• murmur3 - Implementation of Murmur3 hash algorithm used by Cassandra
• oak - A flexible Radix Tree implementation
• radix - Radix Tree implementation
• ternary_search_tree - Ternary Search Tree
• text - A collection of text algorithms
• crystal-linked-list - Implementation of Linked List
• crystalg - A Generic Algorithm Library
• hash_ring - An Implementation of Consistent Hash Ring

Api Builders

• kemal-rest-api - A library to create RESTful API with Kemal

Blockchain

• SushiChain - A custom blockchain platform

Caching

• bloom_filter - Implementation of Bloom filter
• bojack - A non-reliable in-memory key-value store
• cache-hash - A key/value store where entries expire after a specified interval
• crystal-memcached - Implementation of a memcached client
• Nuummite - A tiny persistent embedded key-value store

C bindings

• asound-cr - Bindings for ALSA/libasound
• cairo-cr - Bindings for Cairo graphics library
• crass - Bindings for libsass
• crt.cr - Bindings for libncursesw and crt
• crystal-gsl - GNU Scientific Library bindings
• curl-crystal - Bindings for libcurl
• duktape.cr - Bindings for the Duktape javascript engine
• gphoto2.cr - Bindings for the libgphoto2 library
• icu.cr - Bindings for the ICU library
• libnotify.cr - Bindings for Libnotify
• pcap.cr - Bindings for libpcap
• pledge.cr - Bindings for OpenBSD's pledge(2)
• posix - POSIX/C bindings
• soundfile - Bindings for libsndfile library
• ssh2.cr - Bindings for libssh2 library
• termbox-crystal - Bindings and extension library for termbox (terminal UI library)
• x11-cr - X11 bindings
• x_do.cr - Bindings for libxdo (xdotool)
• clang.cr - Libclang bindings

Cli Builders

• admiral - A robust DSL for writing command line interfaces
• cli - Library for building command-line interface applications
• clicr - A simple declarative command line interface builder
• clim - Slim command line interface builder
• commander - Command-line interface builder
• completion - Easy command line completion engine
• optarg - Yet another library for parsing command-line options and arguments
• OptionParser - command-line options processing (Crystal stdlib)

Cli Utils

• cride - A light CLI text editor/IDE
• dl - Simple utility for download files by URLs from list
• noteesh - Notes and Todo list in command line
• progress - [==..] Progress bar
• progress_bar.cr - A simple and customizable progress bar
• spinner - Terminal Spinner
• terminal_table.cr - Simple ASCII table generator
• todo - Todo list working in command line

Code Analysis and Metrics

• trashman - A simple memory profiler for Crystal applications
• ameba - A static code analysis tool

Configuration

• cr-dotenv - Loads .env file
• habitat - Type safe configuration for your classes and modules
• totem - Load and parse a configuration in JSON, YAML, dotenv formats

Converters

• base62.cr - Base62 encoder/decoder, well suited for url-shortening
• human_file_size.cr - JSON & YAML mapping converter for human file sizes in serialized data
• money - Handling money and currency conversion with ease (almost complete port of RubyMoney)
• moola - Library for dealing with money and conversion (inspired by RubyMoney)
• ms - Library to easily convert various time formats to milliseconds and milliseconds to human readable format
• sass.cr - Compile SASS/SCSS to CSS (libsass binding)
• time_format.cr - Convert time in human readable format with ease
• turkish-number - Turn integers into the Turkish words
• wkhtmltopdf-crystal - Bindings / wrapper for libwkhtmltox (HTML to PDF / image converter)

Database Drivers/Clients

• arangocr - ArangoDB client
• crystal-db - Common db api
• crystal-monetdb-libmapi - Bindings for MonetDB
• crystal-mysql - MySQL connector for Crystal
• crystal-pg - A Postgres driver
• crystal-redis - Full featured Redis client
• crystal-sqlite3 - SQLite3 bindings
• eventql-crystal - EventQL driver
• leveldb - Crystal bindings for LevelDB
• mongo.cr - Binding for MongoDB C driver
• rocksdb.cr - RocksDB client
• tarantool-crystal - Tarantool driver
• rethinkdb.cr - RethinkDB Driver

Database Tools

• crecto-admin - Admin dashboard for Crecto and your database
• migrate - A simpler database migration tool with transactions
• migro - A database migration tool that allows migrations to be specified in either YAML or raw SQL
• micrate - Database migration tool

Data Formats

• config.cr - Easy to use configuration format parser
• crinder - Class based json renderer
• dockerfile.cr - Dockerfile Parsing Library
• front_matter.cr - Separates a files front matter from its content
• maxminddb.cr - parsing MaxMindDB files, including the GeoIP2
• zq - Command-line ZPL processor
• Zip - readers and writers of zip format (Crystal stdlib)
• Gzip - readers and writers of gzip format (Crystal stdlib)
• Zlib - readers and writers of zlib format (Crystal stdlib)
• crystal-toml - TOML parser
• CSV - parsing and generating for comma-separated values (Crystal stdlib)
• INI - INI file parser (Crystal stdlib)
• JSON - parsing and generating JSON documents (Crystal stdlib)
• XML - parsing and generating XML documents (Crystal stdlib)
• YAML - parsing and generating YAML documents (Crystal stdlib)

Data Generators

• faker - A library for generating fake data
• hashids.cr - A library to generate YouTube-like ids from one or many numbers

Development Tools

• guardian - File change watcher for Crystal and Non-Crystal libs
• kemal-watcher - Kemal plugin to watch files and live-reload the browser
• sentry - Watches src files, rebuilds/reruns application on file changes
• sentry-run - Reload code changes using Sentry.run
• Warden - Watches files, run command and a git command if succeed on file changes
• watcher - Watch file changes using File.stat

DevOps

• ansible-crystal - Ansible playbook for installing crystal
• capistrano-kemal - Capistrano Plugin for Kemal
• crystal-cookbook - Chef cookbook for installing crystal

Editor Plugins

• emacs-crystal-mode - Crystal language support for Emacs
• play-crystal.el - play.crystal-lang.org integration in Emacs
• scry - Code analysis server for Crystal implementing the Language Server Protocol
• crystal-spacemacs-layer - Spacemacs contribution layer for Crystal
• sublime-crystal - Crystal syntax highlighting for sublime Text
• Crystal.tmbundle - Crystal syntax highlighting, compile, format command, snippets
• carcin.vim - Vim plugin to provide utility functions for carc.in
• vim-slang - Vim filetype support for Slang Templating Engine
• vscode-crystal - Crystal language support in VSCode
• vscode-crystal-ide - Crystal IDE powered by Language Server Protocol
• vscode-crystal-lang - Formatter, linter and syntax highlighting for cr and ecr files
• vim-crystal - Vim filetype support for Crystal

Email

• carbon - Fun, testable, and adapter-based email library
• crystal-email - Simple e-mail sending library
• CrystalEmail - A RFC compliant Email validator
• devmail - A combined SMTP/POP3-server with volatile mail storage
• sendgrid.cr - Simple Sendgrid Client

Environment Management

• rcm.cr - Redis Cluster Manager
• asdf-crystal - Plugin for asdf version manager
• crenv - Crystal version manager

Examples and funny stuff

• battlesnake_crystal - Tron snake for battlesnake competition
• breakout.cr - Breakout game written using crsfml
• chuck-norris-holy-quotes - Chuck Norris holy quotes
• clamp - Clamp any Comparable
• crsfml-examples - Simple games made with CrSFML
• crystal-benchmarks-game - The Computer Language Benchmarks Game
• crystal-by-example - Crystal By Example
• crystal-mysql-crud-example - Crystal MySQL CRUD example
• crystal-patterns - Examples of GOF patters
• crystalized_ruby - Native Ruby extensions written in Crystal
• exercism-crystal - Exercism exercises
• jihantoro-cr-mysql - Crystal MySQL from scratch sample app
• jihantoro.sd - Crystal & Kemal version of Serdar Dogruyol blog
• kemal-chat - Build realtime applications with Kemal and WebSocket
• kemal-heroku-example - This repository shows, how you can publish your open source apps which powered kemal framework publish as heroku app in seconds
• kemal-mysql-blog - Blog written with Crystal, Kemal and MySQL
• kemal-react-chat - Build Realtime Web applications with Kemal and React
• kemal-vue-chat - Build Realtime Web applications with Kemal and Vue.js
• lattice-core-card-game - A demo web app for (WebSocket-based) lattice-core
• medley - A mixture of music related methods
• os-crystal - x86 Kernel implemented in Crystal
• realtime-todo-app - Realtime Todo application developed with Kemal, Websockets, React, ES2015 and PostgreSQL
• rocky - React Over Crystal Kemal and Yarn
• try.cr - Try monad
• Crystal-Maze - A* Path finding for PNG mazes

Feature Flipping

• flipper - Feature flipping/flags/rollouts. Supports multiple backends

Framework Components

• cr-melon - Class based Http APIs
• crystal-mime - Mimetypes for Crystal
• device_detector - Shard for detect device by user agent string
• Exception Page - An exceptional exception page for Crystal web libraries and frameworks
• graphql-crystal - Graphql implementation
• kave - Kemal API Version Extension
• kemal-auth-token - Kemal middleware to authentication via HTTP header token using JWT
• kemal-monetdb - MonetDB Data connection for Kemal
• kemal-session - Session handler for Kemal
• multi-auth - Standardized multi-provider OAuth2 authentication (inspired by omniauth)
• phoenix.cr - Phoenix Channels client
• request_id - Middleware for generates / pick up a unique request ID for Crystal servers
• response_time - Response time for Crystal servers (pure http server, kemal, etc.)
• spec-kemal - Easy testing for Kemal
• tele-broadcast.cr - Broadcasting module for tele.cr
• Crystal-DI - Lightweight DI Container
• mime-types.cr - A port of the Ruby MIME-types library

Game Development

• cray - Bindings for raylib, an easy-to-use game development library
• CrSFML - Bindings to SFML multimedia/game library
• crystal-chipmunk - Bindings for Chipmunk, a fast and lightweight 2D game physics library
• mos_game - Mini Offline Singleplayer game
• inari - A collection of games using Glove as the game engine
• glove - A library for gaming development

GUI library

• libui.cr - Bindings for libui
• qt5.cr - Qt5 bindings for Crystal, based on Bindgen
• hedron - An extendable GUI library, with markup language capabilities

HTML/XML Parsing

• crystagiri - An Html Reader / parser like Nokogiri Ruby gem
• gumbo-crystal - Bindings for Gumbo, an HTML5 parsing library made by Google
• hq.cr - Simple wrapper for crystal-xml
• modest - CSS selectors for HTML5 Parser myhtml
• myhtml - Fast HTML5 Parser

HTTP

• cossack - Simple flexible HTTP client
• crest - Simple HTTP and REST client, inspired by the Ruby's RestClient gem
• crul - Command line HTTP client
• cryload - HTTP benchmarking tool
• halite - Crystal HTTP Requests with a chainable REST API, built-in sessions and loggers
• helmet - Set security-related HTTP headers
• http-multiserver.cr - Mounting multiple servers via routes (a.k.a. URL mapping)