Since some people (well, er, at least I ) use USB memory sticks to sync calendar data between several computers, it would be nice if there was a feature to synchronize two .ics files. Rainlendar2 would compare the files, and see which modifications are newer, and merge them together. This could be useful at least in my case, where I have three PCs (home, laptop, work), and have Rainlendar2 installed in all of them, with two calendar file active (one local copy on each PC, one on the USB stick).

There could also be a "safe mode" where the user is asked which event should be accepted as the newest one, whether an event should be deleted as it's been marked for deletion, etc.