Audacity projects (.aup files) can be possiibly exported to a multitude of audio formats, including MP3, directly in the Audacity program itself. Otherwise, there is no way how a project of this type can be converted to audio, because it usually contains just references, not the actual multimedia file which is kept separate.
Note: It is likely you will also need Lame and FFmpeg libraries installed, if you already do not have it as part of Audacity installation.Open AUP file Open MP3 file
A free, open source software for recording and editing sounds
Multi-track audio editor for Linux
A multi-track audio editing tool