Back in college, Bottle was where I started to understand how web servers worked. I had written PHP but had zero idea how it worked (or how to write it) and eventually I tried Django, but couldn't configure it to send static files. Once I tried bottle though, it just clicked. It was so simple and I loved that there was little magic. It being a single file that I just dragged into a folder was a BIG part of the simplicity for me, too.
I mostly write nodejs these days (express sorta scratches the same itch), but I have fond memories of bottle. In fact, my old personal site (http://www.superftc.com/) is still a bottle app to this day.