What's a good app to convert AVI video files to something more usable

[DP]

... like a .mov(?). I don't know video to save my ass. I bought a GoPro knockoff and am learning it but it seems to record only in AVI. When I double click on it I get a message that QuickTime can't open it. I did a little searching and found a free app at the App Store called MPlayerX, downloaded it, and bam! It opens and plays just like that. But if I want to put it into a generic or common format that I could send to somebody's email or phone, what do I use to convert it?
TIA.