Code
By "code" I mean computer programs written in Ruby (for Rails) or PHP (for Drupal).
Ruby on Rails is a very influential open source framework for building web sites. I have adopted it for most of my new web-based projects and am glad to share some of the code I find myself using repeatedly.
Drupal is an open source framework for community web sites which is used to run thousands of web sites, including Briar Press, a favorite client of mine. I have made several contributions: original modules, module patches, and core patches (for forms API).