Clementine Music Player https://www.clementine-player.org/
Light-weight system monitor for X.
Newsbeuter is an open-source RSS/Atom feed reader for text terminals. http://www.newsbeuter.org/
qTox is a chat, voice, video, and file transfer IM client using the encrypted peer-to-peer Tox protocol. https://qtox.github.io/
Minetest, an open source infinite-world block sandbox game engine with support for survival and crafting. Also see https://github.com/minetest/minetest_game http://minetest.net/
Calaos server and touchscreen interface
The main repository for the development of the evolution game Thrive. http://revolutionarygamesstudio.com/
An open source re-implementation of RollerCoaster Tycoon 2 roller_coaster https://openrct2.io