I am now taking an on-line course about Machine Learning on CourseRA (Link to the course) which requires Matlab or Octave (an open-source alternative of Matlab) for its programming assignments.
I am taking this course on computers in a library on which I don't have the privilege to install anything. I found there is a portable version of Octave available (see here ) that I can put it on my USB drive and use it on any Windows computer. I haven't tried it yet but it will be very convenient for people who like to take their working environment with them on a USB stick. The caveat is that I can only do this on Windows machines. Also, the portable Octave is based on Octave v2.9.15 while the latest Octave is v3.6.2.The ML class, however, provides an 3.2.4 version (Windows version download link).
From the class forum I learnt that there is an cloud based service which offering access to 3.6.2 version of Octave. Again, I haven't tried it yet but it seems to be an promising way to practice Octave. The Link of the service is here.