• Underscore.lua - A Ruby-like utility library for dealing with iterators, tables, arrays, and functions
• 30log - A minimal OOP framework that supports classes, inheritance, and mixins in only 30 lines
• EncodeInstance - Highly-compressed instance serialization
• BitBuffer Module - Bitwise data storage
• Bitwise Operations Module - Blazing-fast pure-Lua bitwise operations library
• PlayerDataStore Module - Wrapper API around DataStores for saving per-player data
• CFrameInterpolator Module - Easily interpolate between two CFrames
• gloo - A GUI library

Building tools

• F3X's Building Tools - Simple and powerful building tools
• qCmdUtl - An updated version of Animinus' old CmdUtl building tools
• FusiaOS's Map Editor - Simple triangle creator
• Terraingle - More advanced triangle creator
• GapFill & Extrude - Easily fill gaps between and extrude arbitrary surfaces
• Command Panel - Collection of useful commands organized into a searchable panel

Animation

• Roblox animation editor - Official Roblox animation editor

Other

• Seranok's Live Update Plugin - Update your ROBLOX games without shutting down
• DataStore Editor - Read and write DataStores on your places

Other

• Roblox Web APIs - An unofficial list of all known web APIs on the Roblox site
• Roblox Core Scripts - Official respository for Roblox's internal client-side Lua code
• Roblox Bug Tracker - An unofficial bug tracker for Roblox
• Roblox Wiki - The official wiki for Roblox
• Scripting Helpers - Q&A site for Roblox scripting
• Uncopylocked Games Collection - A collection of uncopylocked games
• Awesome Lua - A curated list of quality Lua packages and resources
• Roblox Dev Tips - A collection of useful tips
• Roblox Enhancement Proposals - An unofficial resposository for discussing enhancement proposals
• Skyboxes - A collection of high-quality skyboxes