As mentioned previously, the resources category is an excellent place to find libraries and even plugins/add-ons to assist with Roblox development.
It may be hard to find these resources, so I will put them right here. The Roblox OS server has provided a nice glossary with open sourced tools that you can use for your projects. You can check these out:
ModuleScript loader with reusable and easy unified server-client modules for faster game development on Roblox
Rojo: https://rojo.space/ Rojo is a tool designed to enable Roblox developers to use professional-grade software engineering tools.
Roact: https://github.com/Roblox/roact A view management library for Roblox Lua like React
Rodux: https://github.com/Roblox/rodux A state management library for Roblox Lua inspired by Redux
RoactRodux: https://github.com/Roblox/roact-rodux A bridge between Roact and Rodux
TestEZ: https://github.com/Roblox/testez BDD-style test and assertion library for Roblox Lua
lemur:https://github.com/LPGhatguy/lemur A minimal implementation of the Roblox API in Lua, suitable for running unit tests
Tag Editor: Tag Editor Plugin A plugin for editing and visualizing CollectionService tags.
Source code: https://github.com/tiffany352/Roblox-Tag-Editor/
SublimeText autocomplete for Roblox. Pulls from Anaminus’s API dump.
Be ware that the language definition is a bit funky at this point.
Anaminus’s API dump : https://robloxapi.github.io/ref/ Roblox API dump with fast searching and easy lookup. Very good.
PropTypes : https://github.com/AmaranthineCodices/rbx-prop-types A type checker, originally written for type-checking Roact properties.
Igloo : https://github.com/LPGhatguy/igloo/ A lightweight library for working with immutable data.
luacheck-roblox : https://github.com/Quenty/luacheck-roblox An .luacheckrc implementation for Roblox
selene: https://kampfkarren.github.io/selene/ A modern Lua linter that designed specifically with Roblox development in mind
Touch screen joysticks : A library for easily creating custom touch screen joysticks for mobile games, works with roblox-ts
Source code: https://github.com/Bytebit-Org/roblox-TouchScreenJoysticks
NPM package: https://www.npmjs.com/package/@rbxts/touch-screen-joysticks
fitumi : A unit testing utility for faking dependencies in Lua, works with roblox-ts
Source code: https://github.com/Bytebit-Org/fitumi
NPM package: https://www.npmjs.com/package/@rbxts/fitumi
VSCode Roblox API Explorer https://github.com/evaera/vscode-roblox-api-explorer A Roblox API explorer built right into VSCode.
spr: https://github.com/Fraktality/spr A small spring-based motion library for Roblox UI.
rbx-ts bindings: https://www.npmjs.com/package/@rbxts/spr
luagraph https://github.com/intunderflow/luagraph A library for representing, manipulating and serializing graph data structures
RoactMaterial2: https://github.com/howmanysmall/RoactMaterial2 A material UI library for Roact, originally made by AmaranthineCodices.
A Storybook-like plugin that makes it easy to preview individual UI elements. Especially useful with Roact.
Fabric: https://github.com/evaera/Fabric Fabric provides infrastructure for representing the state of things in your game.
Promise: https://github.com/evaera/roblox-lua-promise An implementation of promises in Luau, with features inspired by bluebird.
Cmdr: https://github.com/evaera/Cmdr A fully extensible and type safe command console for Roblox developers.
BitBuffer: https://github.com/Dekkonot/bitbuffer An efficient way of compressing data, which also works for DataStoreService.
Flipper: https://github.com/Reselim/Flipper An animation library for Roblox based around Motors and Goals. Also features spring-based damping.
evaluate: https://github.com/Nezuo/evaluate A mathematical evaluator for Lua/u.
Roblox-TS: https://roblox-ts.com/ A TypeScript compiler for Luau.
ProfileService: https://github.com/MadStudioRoblox/ProfileService/ A universal session-locked DataStore API.
ReplicaService: https://github.com/MadStudioRoblox/ReplicaService A Roblox state replication system.
There are a plethora of tools to use at your disposal, hopefully you can figure out which tools you need to assist you on your development process.