Enigma is a puzzle game
GemRB is a portable open-source implementation of the Infinity Engine
inputbox password WIN OSX GTK QT Console VCPKG C# Lua R Fortran Pascal
Zoomable user interface (ZUI) with file manager, file viewers and more
INSTEAD - Simple Text Adventure Interpreter.
DOOM / Heretic / Hexen source port with enhanced graphics and UI
Pioneers - The Settlers of Catan
Cross Platform GUI Toolkit
3D driving simulation based on Open Dynamics Engine
A cross-platform interpreter for many point-and-click adventure games
Just a G. U. I. for Prboom / Prboom-plus
A powerful cross-platform and open-source 3-D rendering engine.