Gadgets and other scripts: As a community member I maintain/write many gadgets and site-wide scripts on numerous wikis. I often fix bugs, update versions, clean up and refresh old gadgets etc..
Tools: Maintenance and creation of tools at Wikimedia Labs. User:Krinkle/Tools shows an overview of the different tools I created. I'm also author of the Intuition project (for more info, check the Intuition project pages at translatewiki.net).
MediaWiki.org: Writing technical documentation on MediaWiki.org.
Wikimedia wikis: Although my account is unified on all 800+ wikis, I'm mostly active on Wikimedia Commons and the Dutch Wikipedia, both on which I perform administrative tasks (gadget maintenance, patrolling edits and uploads, counter-vandalism, copyright violations, etc.). See also my global account overview.
Disclaimer: Unless explicitly otherwise stated, any contribution I make to Wikimedia wikis is an act from my volunteer role as member of the community; not a legal or official action from Wikimedia Foundation staff.