Have you tried XFce's Orage?
Oh, I thought it was just a calendar, with no way of adding events.
Now that I found that, it seems alright. I suppose when coupled with a to-do list (maybe one of those post-it notes application) it would do its job. Thanks for pointing it out.
My preference would actually be for sunbird to get integrated into seamonkey...
Thanks for wanting to try to build it, exeterdad.