NITDroid have been running over the years on the N900 and here is the current latest update :

Latest stable Android version running on the N900 is Version 2.3.7. Well this is practically a Gingerbread OS with Google Wallet support. This version is called N12 for NITDroid for the N900

N12 includes receiving and sending SMS successfully. However voice calls and camera are still under development

Here is a list with compatible games being able to run on the NITDroid itself. Overclocking and installation on internal EMMC would be suggested to ensure smooth game play.

And on the day the Ice Cream Sandwich source code is being released, a port of ICS has been done for the N900. Credits to the NITDroid developer drunkdebugger. Here is the link to the video : Video

Let’s hope more updates would come soon and we can get a stable NITDroid to replace Maemo for the N900.