Great, I remember a page which stated that it was sad to have free as in freedom ZMachine languages and interpreters (Inform6, Frotz/Fizmo...) but there were very few text adventures under a libre license. So far, the most known ones:
I know, I play IF games since 2001 and 2002; and my previous gameplays where with the classical ones for ZX Spectrum (in Spanish) and some freeware games bundled with 'shareware' CD's with Winfrotz and later Frotz/NFrotz.
Some GNU user used to have several under libre licenses (even non-ZMachine ones), such as Beyond the Titanic, but he has no working repos any more.
- Spiritwrak
- All Things Devour
- Calypso
- Tristam Island