Evaluation of free UML tools

For a long time now I have been looking for a good & free UML tool that I can use for my personal and non-commercial projects. Recently I finished another survey, which I undertook because I wanted to draw a couple of class diagrams for my open source project Little Go. Unlike my experiences in the past, this time I actually did find a couple of viable tools (see the conclusion), which came as a surprise because, to tell the truth, when I started the survey I didn't have much hope.

Anyway, here I am writing down my findings, possibly for others to read, but also for myself so that I have a starting point in case I ever need to do a future round of evaluation.