Actors

• poolboy - A hunky Erlang worker pool factory.

Algorithms and Datastructures

• datum - A pure functional and generic programming for Erlang
• erlando - A set of syntax extensions like currying and monads for Erlang.
• statebox - Erlang state "monad" with merge/conflict-resolution capabilities.
• riak_dt - Erlang library of state based CRDTs.

Authentication

• oauth2 - Erlang Oauth2 implementation.

Books

• Erlang and Elixir for Imperative Programmers - Introduction to Erlang and Elixir in the context of functional concepts by Wolfgang Loder (2016)
• Stuff Goes Bad - ERLANG IN ANGER - This book intends to be a little guide about how to be the Erlang medic in a time of war.

Build Tools

• rebar - Erlang build tool that makes it easy to compile and test Erlang applications, port drivers and releases.
• sync - On-the-fly recompiling for Erlang.
• rebar3 - A build tool for Erlang which can manage Erlang packages from Hex.pm. See more at rebar3.org

Caching

• cache - In-memory Segmented Cache

Code Analysis

• Concuerror - Concuerror is a systematic testing tool for concurrent Erlang programs.
• eflame - A Flame Graph profiler for Erlang.
• geas - Geas is a tool that will detect the runnable official Erlang release window for your project, including its dependencies and provides many useful informations.

Codebase Maintenance

• elvis - Erlang Style Reviewer.

Configuration Management

• stillir - Cache environment variables as Erlang app variables.

Date and Time

• erlang_localtime - Erlang library for conversion from one local time to another.
• qdate - Erlang date, time, and timezone management: formatting, conversion, and date arithmetic.

Debugging

• tx - An HTML Erlang term viewer, starts own webserver and displays any term you give it from your Erlang node.

Deployment

• docker-erlang - Basic Docker Container Images for Erlang/OTP.

Distributed Systems

• Typhoon - Stress and load testing tool for distributed systems that simulates traffic from a test cluster toward a system-under-test (SUT) and visualizes related latencies.

Geolocation

• erl-rstar - An Erlang implementation of the R*-tree spacial data structure.
• GeoCouch - A spatial extension for Couchbase and Apache CouchDB.
• Teles - An Erlang network service for manipulating geographic data.

HTTP

• bullet - Simple, reliable, efficient streaming for Cowboy.
• gun - Erlang HTTP client with support for HTTP/1.1, SPDY and Websocket.
• hackney - Simple HTTP client in Erlang.
• ibrowse - Erlang HTTP client.
• lhttpc - A lightweight HTTP/1.1 client implemented in Erlang.
• shotgun - For the times you need more than just a gun.

Internet of Things

• lemma_erlang - A lemma for IDEO's Noam internet-of-things prototyping platform.

Logging

• lager - A logging framework for Erlang/OTP.
• lager_amqp_backend - AMQP RabbitMQ Lager backend.
• lager_hipchat - HipChat backend for lager.
• lager_loggly - Loggly backend for lager.
• lager_smtp - SMTP backend for lager.
• lager_slack - Simple Slack backend for lager.
• logplex - Heroku log router.

Miscellaneous

• erlang-history - Hacks to add shell history to Erlang's shell.
• erld - erld is a small program designed to solve the problem of running Erlang programs as a UNIX daemon.

Monitoring

• entop - A top-like Erlang node monitoring tool.
• eper - A loose collection of Erlang Performance related tools.
• Exometer - An Erlang instrumentation package.
• folsom - An Erlang based metrics system inspired by Coda Hale's metrics.
• statsderl - A statsd Erlang client.
• vmstats - Tiny Erlang app that works in conjunction with statsderl in order to generate information on the Erlang VM for graphite logs.

Networking

• barrel_tcp - barrel_tcp is a generic TCP acceptor pool with low latency in Erlang.
• gen_rpc - A scalable RPC library for Erlang-VM based languages.
• gen_tcp_server - A library that takes the concept of gen_server and introduces the same mechanics for operating a TCP server.
• gossiperl - Language agnostic gossip middleware and message bus written in Erlang.
• nat_upnp - Erlang library to map your internal port to an external using UNP IGD.
• ranch - Socket acceptor pool for TCP protocols.

ORM and Datamapping

• boss_db - A sharded, caching, pooling, evented ORM for Erlang.
• epgsql - PostgreSQL Driver for Erlang.
• mysql-otp - MySQL/OTP – MySQL driver for Erlang/OTP.
• pgsql_migration

Package Management

• hex.pm - A package manager for the Erlang ecosystem.

Queue

• dq - Distributed Fault Tolerant Queue library.
• ebqueue - Tiny simple blocking queue in erlang.
• pqueue - Erlang Priority Queues.
• tinymq - A diminutive, in-memory message queue for Erlang.

Release Management

• relx - A release assembler for Erlang.

REST and API

• leptus - Leptus is an Erlang REST framework that runs on top of cowboy.

Testing

• tracerl - Dynamic tracing tests and utilities for Erlang/OTP
• PropEr - A QuickCheck-inspired property-based testing tool for Erlang.

Text and Numbers

• eql - Erlang with SQL or not.
• jiffy - JSON NIFs for Erlang.
• jsx - An erlang application for consuming, producing and manipulating json.
• miffy - Jiffy wrapper which returns pretty maps.
• qsp - Enhanced query string parser for Erlang.
• rec2json - Generate JSON encoder/decoder from record specs.

Third Party APIs

• google-token-erlang - Google ID token verifier for Erlang.
• restc - An Erlang REST client
• oauth2c - An Erlang oAuth 2 client (uses restc)

Web Framework Components

• cb_admin - An admin interface for Chicago Boss.
• cb_websocket_controller - A template for implementing a Websocket controller for ChicagoBoss.
• giallo_session - A session management library for the Giallo web framework.
• simple_bridge - An abstraction layer providing a unified interface to popular Erlang web servers (Cowboy, Inets, Mochiweb, Webmachine, and Yaws).

Web Frameworks

• Axiom - A micro-framework, inspired by Ruby's Sinatra.
• ChicagoBoss - A server framework inspired by Rails and written in Erlang.
• cowboy - A simple HTTP server.
• Giallo - A small and flexible web framework on top of Cowboy.
• MochiWeb - An Erlang library for building lightweight HTTP servers.
• N2O - WebSocket Application Server.
• Nitrogen - Framework to build web applications (including front-end) in pure Erlang.
• Zotonic - High speed, real-time web framework and content management system.

Websites

• Erlang Central - An awesome collections of erlang resource along with live community chat for discussing and seeking help.
• Spawned Shelter - Erlang Spawned Shelter. A collection of the best articles, videos and presentations related to Erlang.
• Erlang Bookmarks - All about erlang programming language [powerd by community].
• Planet Erlang - Planet site/RSS feed of blog posts covering topics across the Erlang ecosystem.