TADS

TADS (Text Adventure Development System) is a programming language and engine intended for interactive fiction.

Some (but sadly, few) of the games written in TADS are Free Software. However it must be noted that the license summary on the main TADS website can be misleading; the primary TADS software is freeware (with source code available) and not Free Software because selling copies is not permitted. FrobTADS, which is used to play and create games on Linux, is not Free Software. Games can still be played in QTads, which is under a GPL license. There is also a web interface at the IFDB : If a game is in the Interactive Fiction Archive you can find its entry in the IFDB and click "Play On-line".