This free software allows you to batch process a music folder's tempi; this means you can analyze the tempo of a lot of files really quickly. Once you have analyzed the files, it then adds the bpm to the files so you can sort by BPM in an audio player like iTunes.
The Amazing Slow Downer allows you to adjust the speed of an audio file so you can transcribe or practice along to an audio file at any speed you want. The pitch of the file does not change while you vary the speed. You can also export the audio file to be whatever tempo you wanted