Brent Simmons is keeping a diary as he works through implementing sync for Vesper, an iOS note-taking app. Building this sort of thing isn’t easy; cf. it took Cultured Code multiple years to implement it for Things. Thus it’s pretty neat that Simmons is breaking it down into understandable chunks:

If you think you need to implement a synchronization system for your application, try to find a shortcut so that you don’t. If you can’t find a shortcut, you could do worse than starting with these notes.