Ren'Py is a free and cross-platform visual novel engine.

you could get it from from extras-devel.

the entry in the app-manager is just a launcher, you could run the tutorial and example game or edit the scripts. but due to a bug, no new project could be created you can still copy an existed project (the best way is copy to the MyDocs directory and create a symbolic link at /opt/renpy/) to the phone and edit it. I don't know if the "Build Distribution" function works or not because i have not tried it on the phone.

porting an existed Ren'Py game to n900 is very easy. just get the linux package of the game. then extract the "game" dirctory and a file named "[gamename].py" (replace [gamename] with the name of the game) from the root of the package to a new location of your game. in the new directory, just run
know issues:

1. the original hot-keys are not worked.
2. no keyboard input in game.
3. the window mode will crop the bottom area.