Even more resources (from unofficial roblox discord)
Programming in Lua/PiL:
https://www.lua.org/pil/contents.html
Lua Manuals (technical/advanced):
Lua 5.0: Lua 5.0 Reference Manual - contents
Lua 5.1: Lua 5.1 Reference Manual - contents
Wiki/Developer resources:
https://developer.roblox.com/articles/Creating-Your-First-Game
https://developer.roblox.com/resources
https://developer.roblox.com/api-reference
https://devforum.roblox.com/c/learning-resources
API reference:
Useful articles/resources:
http://wiki.roblox.com/index.php?title=Custom_chat_GUI
DataStores: Data Stores
How to use DataStore2 - Data Store caching and data loss prevention
Math related stuff: Physics Formulas