Jan Mulder offers "Agenda DS", Which as its name suggests an agenda for the DS.
I do not know if it's finished, but I can not imagine anything to add.
It's like the name says calendar year.
You can browse (correct English?) Through 'your' agenda in the bottom screen.
To add a new activity and press NEW to delete the first one press DELETE.
in the top screen you see the activities in the right order (that's harder to program than you might think).
The first date will automatically disappear when it has been happened.
You can see the current time as well.
And also the time left until the next activity (it always thinks the month has got 31 days).
The dates are automatically saved to your FAT and they will automatically load too.
When the dates are being loaded it might be possible it has some bugs.
It works better in an emulator but then you can not save.
The dates in the browsing part are not correct.