I am pretty sure he asked for alternative alarm clock software, not for a list of which Nokia customers have been able to use the standard alarm without trouble...

Thread starter, if you have the knowhow, you might consider if the broken alarm software is a symptom of a bigger problem, like your installation may be partially corrupted. If so, or if you think this is a big enough a deal, you may consider reading up on reflashing your telephone to get back to a clean installation. Hopefully that may help.

If not, I don't think there's a lot of finished clock projects for the N900. The one I know of is the Flip Clock. Or you could look in the Maemo garage and see if anything there is both made for the N900, and in a working condition.