Do you need to convert AAC to MP3? M4a to MP3? MP4 audio to MP3? Your favorite player doesn't support M4a audio? Then take a look at the new tool from ManiacTools, Free M4a to MP3 Converter.
The program supports a number of input formats, like the above mentioned AAC, M4a, MP4 audio, M4b (audiobooks), and some other MPEG-4 based audio formats. You can convert those types of audio files to MP3 or uncompressed WAV. The latter can be used as an intermediate format for further converting (with tools like AudioConverter Studio).