Sarien is a free GPL
for the earliest Sierra
graphic adventures (those who are written with the AGI
system). Some examples of AGI games are King's Quest
(1, 2 and 3), Space Quest
1 and 2, and Police Quest
Sarien has several display drivers and can run on a variety of platforms, for example in X11 on Linux. It also supports 3 channels of PCM sound. Although (at the time of writing) it has not reached version 1, it can be used to complete several games from start to end.
Of course, you need the original data files to play the games.
The homepage is located at http://sarien.sourceforge.net.