Platform

Abuse (C++, Lisp, Public domain, GPL-2.0, WTFPL, mature, inactive since 2011)
CaveExpress (C, GPL-3.0, mature)
Data Storm (C, Apache-2.0, mature, inactive since 2017)
Dave Gnukem (C++, GPL-2.0, mature)
Executive Man (JavaScript, Custom, mature, inactive since 2017)
freegish (C, GPL-2.0, beta, inactive since 2017)
FreePrince (C, GPL-2.0, beta, inactive since 2011)
freeVikings (Ruby, GPL-2.0, beta)
glPortal (C++, zlib, beta)
Open Surge (C, GPL-3.0, beta)
Smash Battle (C++, ?, beta, inactive since 2011)
The Legend of Edgar (C, GPL-2.0, mature)