Agender is a cross-plataform schedule/calendar tool. It was written to be small, simple and work on any computer with any OS. Agender is free software, it is licensed under the GNU General Public License.
With Agender you can associate some notes with a date or with no date in particular if you mark the note as sticky, you simply start it and it will create a task-bar icon and stay in the background, without annoying you, it can also be configured to run on login.