Sagemath, or just Sage, a Free Software computational mathematics software, has a hosted service that’s in beta testing phase. Sage is a Free Software alternative to Matlab, Magma, Maple, and Mathematica.
It is cross-platform and free to download. The Cloud-hosted service aims to provide users a stable platform for doing computational mathematics tasks they would normally be doing on a local installation of Sage in the Cloud.
Access to the service is available after a free registration at cloud.sagemath.com. William Stein, a professor of mathematics at the University of Washington, is the principal author of Sage and is also responsible for the hosted service.
While the Cloud service is still in beta, Sage 5.11, a new edition of the standalone software, was released a few days ago. The download options are available here. If you are interested in applications like Sage, you might want to read 4 Free Software alternatives to Matlab. This screen shot shows the interface for uploading data files to the Sage hosted service.