Cards

Aisleriot (C, Scheme, GPL-3.0, mature)
BetterSpades (C, GPL-3.0, beta)
Card Stories (JavaScript, Python, AGPL-3.0, beta, inactive since 2012)
Deer Portal (C++, zlib, beta)
Forge (Java, GPL-3.0, mature)
Gnome Hearts (Python, GPL-2.0, mature, inactive since 2015)
Heroes of Civilizations (C++, C#, GPL-2.0, beta)
JSkat (Java, GPL-3.0, Apache-2.0, beta)
Libre: The Open Source Card Game (Python, AGPL-3.0, mature, inactive since 2010)
Magarena (Java, Groovy, GPL-3.0, mature)
NetMauMau (C++, LGPL-3.0, mature, inactive since 2015)
OpenEtG (JavaScript, MIT, beta)
OpenTriad (Java, GPL-3.0, beta, inactive since 2017)
PySol (Python, GPL-2.0, mature, inactive since 2004)
Simple-Solitaire (Java, GPL-3.0, mature)
Tressette (C++, GPL-2.0, mature, inactive since 2017)
Wagic, the Homebrew (C++, C, Objective-C, 3-clause BSD, beta)
Walic (Kotlin, Apache-2.0, mature)
Wizards Magic (Python, GPL-2.0, mature, inactive since 2012)
XMage (Java, MIT, mature)
XSkat (Java, Custom, mature)