Gnote is a Tomboy fork written in GTK.

Use Mono if you want. It is a bug of mine not because it comes from
Microsoft but because Microsoft won't come clean on it. If it is legitimate
as de Icaza says then the solution is simple. Microsoft needs to say that it
is free for everyone to use and it should be released under one easy to
understand open source license. Both of these things are possible, but
instead we have uncertainty. This is intentional to my way of thinking
because they want to continue their accusations of IP infringement.

The other thing that many people would like is for Mono to be removed from
free to non-free in the repositories. That would place it in the same boat
as flash and other things that are proprietary or patent encumbered.

Give Gnote a try. It forked from Tomboy a couple of years ago and the
developers had high hopes that it would replace Tomboy in many
distributions.

http://en.wikipedia.org/wiki/Gnote