Maemo
From Rory.wiki
Repositories
The N900 ships with just the basic repositories enabled. you can enable "extras" from the GUI, but for a lot of pen tester type or dev type packages, you'll need extras-testing and extras-devel. That adds quite a few useful packages, including OpenVPN.
Still doesn't currently (Dec 09) have things like nmap and ruby 1.9.1 so if you need to get extra stuff working you can compile it yourself :)
Compiling packages
The Maemo SDK uses scratchbox to create an environment for cross-compiling apps for Maemo on a PC (which is faster than doing it on-device and saves you space for dev. tools).
Easiest way to get started it to set up the Maemo SDK and then go from there. One option apparently would be to install the debian repositories into your scratchbox environment, install the source of the package and re-compile for the architecture. I had a look at that for ruby1.9.1 but very quickly ran into problems with dependencies not compiling properly.
So next choice is to get the source and compile yourself. There's good documentation on the wiki and a specific guide on making application packages.
One problem is lack of space in the root file system. To get around this you could use the maemo-optify-deb command once you've create your initial .deb file, the maemo-optify package is available in extras-devel and isn't needed on the target device just the system that creates the package. Worked pretty well for me so far.
So far (Dec 09) I've got nmap working ok.
Debs
Needless to say these are totally unsupported and have only been tested on an unscientific sample of 1 Nokia N900 (mine). In particular watch out you don't run out of room on any of your partitions (although there's 32GB of space on an N900 not all of it can traditionally be used for application installs).
