Ask HN: Best way to do a cross-platform Python GUI in taskbar (eg Dropbox)?

I want to persistently run a small Python program on the user's computer with an icon in the taskbar, that will work on Windows/Linux/OSX, with a few items in the pop-up menu.

Basically the exact same way Dropbox works as far as GUI goes.

It just needs to have the program running all the time from boot, monitoring something, and let them click the icon to open a little menu that has 2 entries to run functions in the program, and 1 entry to open a Settings/Config window.

I'm open to not using Python if there's a better way, but I was hoping to use this project to learn more Python, so that's preferable.