Adventure

AdaVenture (Ada, GPL-3.0, mature)
Childsplay (Python, GPL-3.0, mature)
Colossal Cave Adventure (Python, Apache-2.0, mature)
Der Clou! (C, Custom, beta, inactive since 2017)
Digital: A Love Story (Ren'py, CC-BY-NC-SA, mature)
Dragon History - Dračí Historie (Pascal, Script, GPL-2.0, mature, inactive since 2010)
Fanwor (C, GPL-2.0, mature)
Free in the Dark (engine) (C, C++, GPL-2.0, beta)
GameLV (C++, GPL-2.0, beta)
Head over Heels (C++, GPL-3.0, mature)
Heart of the Alien (C, GPL-2.0, beta, inactive since 2005)
javascript-E.T. (JavaScript, Assembly, MIT, beta, inactive since 2017)
Morpheus Web Remake (Javascript, MIT, beta)
Murder In The Public Domain (C++, GPL-3.0, mature, inactive since 2013)
Privateer - Gemini Gold (C++, GPL-2.0, mature, inactive since 2012)
ResidualVM (C++, GPL-2.0, beta)
Sentient Storage (Python, Public domain, mature)
Sintel The Game (Python, MIT, beta, inactive since 2014)
Star Maiden Astraea Rio (Ren'py, CC-BY-NC, mature)
star-control2 (C, C++, MIT, mature)
terrarium (C++, GPL-2.0, beta)
twin-e (C, GPL-2.0, beta, inactive since 2015)
TwinEngine (C, GPL-2.0, mature, inactive since 2015)
uninvited (C, C++, Artistic License-2.0, beta, inactive since 2016)