ffmpeg

I was looking for some freeware to quickly convert audio files, trying to avoid free online converters that I don't trust with my files, and I found this gem.

A command line tool that can convert audio as well as video.

For example, to convert a file called "rain" from wav format (or whatever) to mp3 format (or whatever), just run the following command in terminal from the directory that holds the original:

ffmpeg -i rain.wav rain.mp3

That's it!

Read more about it here. See it in action below.