Lots of people live on two desktops. Mac at home, Windows at work. Or the other way around. Or a Mac mini in the studio and a gaming Windows tower in the basement. The note app that ships with each one is excellent — inside that one ecosystem. The moment you cross, the workflow falls apart.
Apple Notes does not run on Windows. Sticky Notes does not run on macOS. You can wire up a third-party note suite, but you wanted a sticky note, not a knowledge management system. So most people end up emailing the note to themselves, or pasting it into a chat thread, or just retyping it — and then the “note” lives in two places and they fall out of sync.
Sticki.ly is the smallest possible answer to that one problem. The same sticki shows up on both desktops, in the menu bar and the system tray respectively, and stays in sync without you having to remember anything.