Bitbucket shaved off too many features from their public profile interface in early 2016, so I much more prefer to show my own list of projects here (using their API). Only some of the latest pet projects are featured here, see the section below for the full list.
Since my preferred VCS is Mercurial, I put my code here.
Also, a big chunk of ExtJS experience comes from this project.
Projects hosted here also get my attention, but not that often.
One of the most famous open source projects that I contributed to is this. Not only my favorite VCS, but also a great project to learn new technical things and workflows.
Also I'm a reviewer for hgweb.
It's similar to Project Euler, but most of the problems are more bioinformatics-related than maths-related.
Improving localization is essentially improving user interface. When I was just starting as a translator, I used Rosetta, which is Launchpad's translation service. And it still tracks my translations, diligently, even though I don't use the system.