Few programs have dominated an open source category like Audacity. It works so well that many people don’t even try other programs — especially for podcasts and “Powerpoints.”
Audacity can import or record multiple tracks, trim audio, level audio, fade-in and out, cut-out mistakes, etc — all the basic features you need for podcasts, radio spots, presentations, etc. It has more audio-processing filters and the ability to add even more but I rarely use any of those.
It can export to WAV, WMA (Windows), AIFF (Apple), FLAC (cool) and most importantly, MP3.
A few years ago, I had a radio production studio with a couple of expensive commercial editing programs but I found Audacity to be the quickest for simple productions — like two or three voices and a music track.
I challenged one of my technicians to produce a song with Audacity but he didn’t like it, saying it gave him timing problems. (three or four musicians?). More recently, I tried to use Audacity as a music sequencer and didn’t like it for that, either. I have also had problems with very long, single take, recordings (like over an hour.)
But, for simple audio production, it’s a very useful program, rivaling commercial products. Highly recommended.