A reasonably complete port of prboom is in extras-devel.

Remember, software in extras-devel could cause data loss, hair loss, spouse loss, global warming, or male pattern baldness. Don't enable the extras-devel repository unless you know exactly what you're doing, and don't leave it enabled on your N900 or you're just asking for trouble.

Usage

If you do decide to install it, you'll need an iwad file. I've been using the one from freedoom, which is, coincidentally enough, free. Put it in /opt/doom/wads. You can also use the doom1 demo wad by installing the doom-wad-shareware package from extras-devel. While you have the repo enabled to install prboom, get a root shell (Ctrl-shift-x to open shell, type "root" (you did install the rootsh package, right?)) and type Controls

Fn - fire (left thumb goes here)
Shift / Z - strafe left/right (below left thumb)
Ctrl - run (above left thumb)
a - strafe (right of left thumb)

top row of keyboard (qwertyuio) - weapon keys (correspond to number keys)

, - best weapon (appears the map failed, hmm), also escape menu
. - next weapon
space - activate
backspace - menu/back to previous menu
p - pause

Basically the controls are clustered around the fire button on the left (Fn) and the arrow keys on the right. Localized keyboards will probably need the workaround described in my earlier post.

Known Issues

• No default iwad is installed; see above.
• Probably suffers from Nokia's localization bug AKA "Dude, where's my up arrow key?". Workaround described here. There's also an applet to do this for you.
• No throttling or pausing on loss of focus or screenblank: don't leave it running in the background while you go off and do other things or your battery will be sad.
• Mouse control breaks the ability to use the on-screen exit button and generally isn't helpful. Leave it the way it is set: OFF.
• No music. Sorry.
• I need to add metra's patch to bypass the exit confirmation so you can simply tap the 'X' in the corner. Right now you have to push 'y' after doing that.

Note to would-be app maintainers:

I was careful to document everything i did as i prepared the ubuntu/debian package for maemo. Anyone who is looking for a bit of a working example on how to start with maemo packaging starting from a debian source package can grab the source package in the SDK scratchbox
and look at the changelog in ./debian.