Does anyone know of a Linux converter that does not take forever and three days to convert a movie?

ffmpeg

it has been multy threaded for the last few years

or
mencoder

Also ensure some hardware video acceleration is put to use; using vaapi or vdpau for ffmpeg/mencoder.

Please read the "How to ask a smart question" and "Question Guidelines" links in my posting signature.

Your question is incredibly vague. You don't tell us what version/distro of Linux, what you actually mean by "forever and three days", what the input length of the movie(s) in question are, what you're converting them with NOW, what quality you want, etc. Common sense says that if you lower the resolution, delete audio tracks, etc., you'll get a quicker conversion, than if you're trying to capture a full Blu-ray movie in HD with 4 different audio tracks and subtitles.

Provide details and ask a clear question, and we can try to help.