Just one thing... "PC" is definitely not a OS name and "Mac" usually refers to the hardware by Apple. "Microsoft" is not a mobile OS name either.
I think you meant "Windows, Mac OS X and GNU/Linux" in place of "PC" and "Mac", and "Mobile - Windows Phone/Windows Mobile[dead]" in place of "Mobile - Microsoft". Just thought that if you want to take this as a serious thing, it's better to pay attention to detail and be precise.

And as gweedo said, sqlite is definitely not a good choice if they are going to hold a big amount of transactions (much less the whole blockchain).