HN has really motivated me to start thinking about side projects seriously, even if just as learning exercise or solving my own problems. I only just started publishing them a few months ago, but I've had a lot of fun these:

Chroma https://github.com/seenaburns/Chroma - Python color handling and manipulation library

Desaturate https://github.com/seenaburns/Desaturate - Menu Bar app to force Mac OS X into grayscale display

Tungsten https://github.com/seenaburns/Tungsten - Wolfram Alpha API wrapper for Python

Open URLs In Tabs https://github.com/seenaburns/Open-URLs-In-Tabs - Port of John Gruber's OS X service to open links in tabs, modified to work for Chrome (/ your default browser).

Desaturate is definitely my favorite. Now for 2013, I have to learn to comment more and write more.