I would love to find out how to compile a list of seldom-used applications automatically myself, but I suspect it may be a bit tricky (the relation between a "package" and an "application" is not that straightforward, for one thing; some programs are used by other programs, a package can contain multiple executables or none at all; some applications may actually be started automatically each time you boot but never actually used by you, and so on).
What I sometimes do on machines with little RAM/disk space (just did it yesterday on an original EeePC with a 4Gb SSD):
- install synaptic
- in the left pane, select to show all installed applications
- go through the list, marking the packages I don't need to be removed
- after the apps are uninstalled, run
sudo apt-get autoremove to uninstall any libraries installed as dependencies of the uninstalled applications.
The process is a bit time-consuming (maybe an hour or so) and is only justified if you're really tight on disk space (or just having fun). On the other hand, it allows to remove more than any automated process would - for example, I was never going to use bluetooth or printing on that machine so I removed
cups packages, which otherwise are actually in use by the system.
It is possible to break your Ubuntu if you're not careful, but otherwise it's a great learning exercise.