Mousotron is a free system monitor which keeps various statistics on your mouse and keyboard use.
The program doesn't record the keypresses themselves, or otherwise compromise your security. Instead it maintains figures like the total number of left, right and double-clicks, mousewheel scrolls, the number of keystrokes, and the distance travelled by your mouse cursor.
At its simplest, this could just be a fun experiment, a way to find out how many keystrokes you really enter in a day, or whether you're busier than a friend or colleague.
Mousotron can have more serious applications, though, in particular related to RSI (Repetitive Strain Injury). It could help you find out whether one program requires more keystrokes or mouse moves than another, for instance, or provide feedback to help reduce the mouse/ keyboard actions you're taking.
We suspect there are other possibilities, too. These figures will presumably have a fairly consistent pattern for each user, at least with the same set of applications (one person may always use mousewheel scrolls more, someone else relies on right/ left clicks). If you had Mousotron data from a few people on their own PCs, maybe you could match that with Mousotron figures on a public computer, to find out who's been using it, and when.
Whatever your interest, the program is very configurable. You're able to choose exactly what's recorded and how, and even upload the data online if you'd like to compete with others.
It's not the most essential of programs, but if you have a need to monitor mouse or keyboard statistics then Mousotron will get the job done.