Windows only: WinWorkBar is a free, lightweight application sidebar complete with flexible to-do list, notes, calendar, and more. It may not look like much, and its meager 600KB download size and 6MB footprint may not sound like much, but this little sidebar application packs a lot of punch. You can customise keyboard shortcuts to quickly perform any action (e.g., show/hide the sidebar or create a new note or task), assign tasks and notes to any day or range of days (complete with reminder alerts), create repeating tasks quickly and easily, and automatically toggle the application's visibility so it's only taking up space when you want it to be. WinWorkBar doesn't do any fancy syncing (or anything all that fancy, really), but if all you're looking for is a powerful yet lightweight and unobtrusive to-do list manager, calendar, and notes application, WinWorkBar fits the bill. WinWorkBar is free and open-source, Windows only.