Tomboy : Simple note taking - because I looked it up again: it now also works on OS X. However, it is still extremely buggy (scrolling artifacts, no standard key bindings, you have to blindly fiddle with the bottom right corner to resize the window, the handle is missing). It is based on rather fresh libraries that are not yet really up to the best Mac-UI standard. But to access notes from Linux Tomboy and sync via Dropbox, it is sufficient.