All you need is Audacity and the FFmpeg library. I had issues using the most current FFmpeg (3.2.4) but the 2.2.2 binary worked just fine.
When importing the stream names are invisible but you are able to select them.
The first stream (stream 0) is the whole track. The rest (1-4) are the individual tracks.

NI's free pack of 65 stems made from Maschine expansions.

Export as .aiff or .wav and chop/use in your DAWs, samplers and hardware or re-encode as mp4 and use as ringtones...

Hacking Stems / Extracting Instrumentals
Everyone loves the STEM concept, and who has not wanted to break down a track and take out the bass, vocals or drums. In my experience, this is often something that you could do once, and not worry about live. It would make sense then to create a permanent “edit” of your stem that has those parts removed and not bother with isolating things in the DJ set.

Here are the steps you need to take in order to break apart a Stem file and isolate the parts outside of Traktor (or Mixed In Key’s Flow 8 Deck, which is the second DJ software to support Stems playback). First, get your system set up with the right software:

1. Download Audacity (PC/Mac) and download FFmpeg Library for Audacity (PC/Mac) (both are free)
2. Go into Audacity’s Preferences > Libraries
3. Click on “Locate” next to “FFmpeg Library” select “libavformat.55.dylib” which will be contained in the FFmpeg download

Now let’s import the Stem file into Audacity and isolate them:

1. Import the Stem .MP4 file (it will be fairly large and take a few minutes)
2. Select all five of the streams (this will include the master stereo mix and each of the four stem parts)
3. File > Export Multiple in Audacity (use AIFF or WAV and number them so you can keep track)

Make A Custom Instrumental From A Stems File
To make your own custom instrumental, bring the files into Ableton:

1. Drag all the files into Ableton Arrangement view (hold down the CMD/Ctrl key to easily separate them into their own audio tracks)
2. Adjust the session to the track BPM and line up the beats. Make sure the individual audio files are not warped
3. Remove the stereo master track

Finally, fine tune your instrumental so it is more playable:

1. Move a portion of the drum track/beat to the first 8 counts
2. Isolate your parts and add mastering as needed/wanted
3. Bounce out as WAV or AIFF with the BPM in the file name for quick reference

Source: DJTechtools

 

Great share. In relation, seems this is also helpful.

http://blog.beatunes.com/2015/09/destemming-stems.html