AthenaOS

Open-source Pythonic Assistant.
Not actively worked on currently.
Source

Xyzzy

A batteries-included text adventure engine, written in Arturo.
It is designed to be everything you need to make a terminal-based text adventure/RPG, where creating new stories is as easy as writing some JSON objects. Other planned features include support for custom interfaces, making it easy to create GUI's on top of it.
Source

WIP Project (Codename Jade)

A flexible framework in Lua to easily build games with a pre-made entity manager, scene system, map editor, and GUI systems.
It is a set of tools built on top of Love2d, and also used to make a game myself at the same time.
Source

Synthlink

Framework for showing generic now-playing status in Discord, automatically.
It works by pulling the current playing media via the MPRIS protocol on Linux systems, which can detect from almost any media source, including web browser instances, and then pushes that data to Discord over RPC, meaning it can edit your status without requiring any access to your account.
Source