well don't know if it is even an appropriate answer to OP's post, but here are two apps I really miss from my old N95 8GO and could not find for my N900. Those wonder was (and I still use them on this good old N95):
An app able to measure and calculate any areas thanks to the GPS.
You walk (or drive) with the phone, and you "click" some points (kind of way-points), and then the app compute the perimeter and the area of the so deliminated surface. (the larger the area is, the most accurate result...)
5he other app was a game: a kind of FPS where you are a ninja throwing shurikens (kind of steel stars) towards ennemies in a quite photo-realistic landscape... The thing that made this game a must have is that you threw the shurikens by waving your hands over the camera lens like idf you were physicaly throwing them! A very cool sensation!

So, if this could give ideas or inspiration to talented devs around for our beloved N900.... I sadly do not have the needed free time for that.
Thanks