CloudConvert
CloudConvert is one of the tools that I'm simply thankful it exists. It's a web based tool that can convert anything to anything. Do you have an ePub than you want to be in Kindle format? It can do it. Do you have some FLAC files that you want in AAC? CloudConvert is your tool. With nothing to install, it's incredibly easy to use. Since it's a web based system, it's not relying on your computer hardware in order to convert. This means it potentially can move a lot faster without slowing down your local machine.