Sage is a free open-source mathematics software system licensed under the GPL. It combines the power of many existing open-source packages into a common Python-based interface.
you can read more about sage here http://www.sagemath.org/tour.html
unfortunately sage is not available in the Ubuntu repositories and in-fact any repositories as a .deb package. ( at the time of writing this). did you say compiling? dont even go there i tried building it. and failed woefully. fortunately i found a nice and easy to install it on Ubuntu. there is a binary package already compiled for Ubuntu. which makes installation on Ubuntu quite easy and straight forward.
first we download the ubuntu binary here http://www.sagemath.org/bin/linux/32bit. the guide is based on version 3.1.4 so i just did
the above link seem to be broken. although i have not tried it. but this link should work
wget -c ftp://ftp.sun.ac.za/pub/mirrors/www.sagemath.org/linux/32bit/sage-3.4-linux-PentiumM-ubuntu-8.04.1-i686-Linux.tar.gz
wget -c ftp://ftp.sun.ac.za/pub/mirrors/www.sagemath.org/linux/32bit/sage-3.4-linux-Ubuntu_8.10-i686-Linux.tar.gz
once downloaded . i untar it (extracted the archive)
in my case
tar xzvf sage-3.1.4-ubuntu32-intel-XEON-x86-i686-Linux.tar.gz
then i moved it to /usr/local/src/
sudo mv sage-3.1.4-ubuntu32-intel-XEON-x86-i686-Linux /usr/local/src
then i copied the sage script in to /usr/local/bin
sudo cp /usr/local/src/sage-3.1.4-ubuntu32-intel-XEON-x86-i686-Linux/sage /usr/local/bin
then i edited SAGE_ROOT in /usr/local/bin/sage to point to /usr/local/src/sage-3.1.4-ubuntu32-intel-XEON-x86-i686-Linux
gksu gedit /usr/local/bin/sage
modified it to look like this
# Set SAGE_ROOT to the location of the sage install.
i modified the sage root directory permission settings
sudo chmod -R 755 /usr/local/src/sage-3.1.4-ubuntu32-intel-XEON-x86-i686-Linux
now run you can run it
to get a webbased ui
hope someone finds this useful.