Vorbis is a free as in freedom lossy audio codec project headed by the Xiph.Org Foundation. It is the only good free alternative to the MP3 file format. It is almost always used with the Ogg container and is therefore called Ogg Vorbis.
 Convert MP3 to OGG
Converting from one lossy format to another lossy format is never a good idea. You may want to do so regardless of it being utterly nonsense for some idealistic or practical reason. Here's how:
You need mpg321 vorbis-tools
mpg321 input.mp3 -w - | oggenc -o output.ogg -