A colleague and I have spent a few years developing a really cool Matlab application, MDLcompress. Within Matlab, I can type \"MDLcompress(\'filename.txt\')\" and it will tell
If you can afford to lose some of Matlab's more powerful proprietary features, there are several open-source numerical computation engines that use syntax mostly compatible with that of Matlab. One of the most mature of these is GNU Octave.
There are several examples of online Octave interfaces. Octave Online is a new interface that supports a live prompt and an online editor. I am a member of the team developing Octave Online. You can find more examples of online Octave interfaces on the Octave wiki. The Octave mailing list is a good resource for prior online Octave projects.