Various projects and libraries that aren't standalone but merit some mention.
Over the course of my career I've either created or contributed to a number of open source projects, including these.
Pypeline is a Python library for rendering various text markups (Markdown, ReStructed Text, Textile, Creole, etc.) into HTML. SourceForge uses Pypeline for rendering READMEs in the file and code browsers.
Upcoming.js is a Javascript component that renders a Google Calendar into a lightweight, customizable list of upcoming events. Created to display a list of upcoming events on a church web site after I found Google's embedded calendar solution too heavyweight and not easily integrated into the site design.
Apache Allura is the development collaboration platform that powers SourceForge. Now part of the Apache Software Foundation, I helped develop the initial codebase.