Commander Genius aka CloneKeenPlus is an engine which interprets Commander Keen 1-4.

Release notes from Pickle:

Ive updated the all of the archives for the latest source code for cgenius.
One notable feature for this update is support for streaming the hqp ogg files, which are included (all except for gp2x too slow, but ogg support is compiled in if you have to have it)
Also added support for a the caanoo.
Also includes enhanced graphics replacements and also includes keen1 and keen4 sharware data.
Keen4 work has begun you can jump and run through levels and collect items so far.

http://dl.openhandhelds.org/cgi-bin/gp2x.cgi?0,0,0,0,20,2832