Flask is a wonderful Python microframework for server-side web development.
I haven't used Flask for a year or so, outside of the horrifying, grindy refactoring I've been doing at work, so I decided to hack together a little Tumblr clone. Overall, this thing took me about two days to complete.
This was also a great chance to brush up on using the SQLAlchemy ORM, as well as learning a few Flask extensions I want to use in some future projects (Flask-Login, Flask-Assets), and some fun features of Jinja2 that I'd never used before.
Since this is a random side-project, I didn't use a heavy CSS framework, but just hacked up the CSS on-the-fly; I think that gave the UI a nice early-to-mid 2000s feel.