A decently featured microblogging web application written in Python and Flask that I'm developing in my Flask Mega-Tutorial series that begins here.
Note: This is an old version! For the current version, go to https://github.com/miguelgrinberg/microblog.
The tutorial referenced above explains how to setup a virtual environment with all the required modules.
The sqlite database must also be created before the application can run, and the db_create.py script takes care of that. See the Database tutorial for the details.
To run the application in the development web server just execute run.py with the Python interpreter from the flask virtual environment.
