You can get GMouseTool both in binary and source code form. Choose what fits better to you.
Pre-built binary packages
Note: The binaries above work with the following Ubuntu versions: 9.10, 10.04, 10.10, 11.04, 11.10, 12.04 and 12.10.
In order to get the latest source code you must run the following command:
bzr branch bzr://gmousetool.bzr.sourceforge.net/bzrroot/gmousetool