NOTE: Hamster is being maintained at the moment.
Details here: http://projecthamster.wordpress.com/2013/05/13/hamster-is-looking-for-a-new-maintainer/

Hamster can be found packaged in most distributions. The instructions below
are for installing from sources for testing and development purposes.

The instructions are mix between Gnome 2 and Gnome 3, so, errm, just bear with
us.

hamster-applet → hamster-time-tracker clean up

Previously hamster was installed everywhere under hamster-applet. As
the applet is long gone, the paths and file names have changed to
hamster-time-tracker. To clean up previous install follow these steps:

git checkout d140d45f105d4ca07d4e33bcec1fae30143959fe
./waf configure build --prefix=/usr
sudo ./waf uninstall

Dependencies

Debian-based: apt-get install git-core gettext intltool python-gconf
RPM-based: yum install git-core gettext intltool gnome-python2-gconf

Installing

./waf configure build --prefix=/usr
sudo ./waf install

After that make sure that the old daemons aren’t roaming around:

killall hamster-service && killall hamster-windows-service

Now restart your panels/dockies and you should be able to add hamster to your panel!