Recs.
Updated
Tomboy is a note taking application for Linux, Windows, and Mac. There's also Tomdroid for Android and Rainy to sync between them.
SpecsUpdate
Pros
Cons
Con No longer supported
Tomboy and its clones were brilliant note-taking applications before most of the other offerings were the beginning of an idea in some developer's head. There was cloud support with Ubunto One before they dismantled that offering. The apps offered links between notes, rich text, and an easy-to-work-with xml saving format that made it easy to backup and unlikely you would ever lose your data should program support cease. Unfortunately and inexplicably, support has ceased. Tomdroid never reached feature parity with Tomboy, and neither of the two is being developed anymore. The clone, gnotes, is still available for linux, but without any other platform support or easy cloud syncing it's just not as useful as it was before smart phones killed handheld linux devices.