Please elaborate in more detail, so we can try to help. While it is true that the N900 is still missing a few major apps (Office Editor, Ovi Maps with Navigation), it also offers many alternate solutions:

• "Office": Documents To Go Viewer Edition
• "MSN": If you mean the chat, there is a plugin available for the conversations framework. The N900 has ONE app for all different chat networks, no need for individual apps.
• "OPERA": MicroB is a vastly superior, real browser IMHO. Or what functions are you missing form Opera?
• "Core Player": Using SiB/Mplayer, the Extra Codecs package and the built-in Media Player offer a superior replacement.
• ".RAR": unrar is available as command-line tool. Do you really need the .rar part or just unpacking? There is also 7zip available btw.
• "Iplayer": If you mean the BBC iPlayer, then I believe there is also some solution around.

Please list some of the "Many More", this could be helpful in creating development ideas.