PX/IF is an abbreviation for Perl/XML based interpreter for Interaction Fiction. It is a framework to create IF games developed by Hannes Schueller. Objects, characters, locations, events and verbs are defined in simple XML structures, falling back to Perl code for more advanced game logic.
PX/IF was written in 2001 for the purpose of having an engine which could run games on a server, accessed through a regular web browser. The only finished I/O module only allows for playing games in a terminal, though.