On December 3rd SAGE was released. Per the SAGE home page:
"Use SAGE for studying a huge range of mathematics, including algebra, calculus, elementary to very advanced number theory, cryptography, numerical computation, commutative algebra, group theory, combinatorics, graph theory, and exact linear algebra."
SAGE is a large collection of libraries (chunks of computer code written for specific tasks). It is written in the wildly popular Python scripting language. SAGE libraries can be accessed by custom Python programs and SAGE can interface to Mathematica and other popular mathematics software.
The great thing about SAGE is that it is open source, which means it's free and thus accessible to a much larger percent of the population than the commercial Math software.
To be honest, I'm not quite sure how a non-programmer would use SAGE as I have not yet downloaded the software. My sense is that there's quite of bit of work that will need to be done in terms of documentation and user interface before SAGE will be accessible to end users. I was a programmer for many years and have worked with scripting languages (of which Python is one) and I've worked extensively with Linux so I'll probably be comfortable in the bowels of the system but many people won't be. The SAGE download page provides downloads for Mac OS X, Windows using the VMware player, and Linux. There's some browser interface mechanism, through browsers plugin, I believe.
There's a slashdot discussion taking off.
I'll write more as I gain experience with SAGE. I'd love to hear from anyone who gets this running before I do.