Gitstalk - Discover what your favorite GitHub users are up to
GitNews Web - Trending repositories from GitHub, HackerNews & Reddit
Octoview - The missing preview feature for GitHub
LibHunt - LibHunt tracks mentions of software libraries on relevant social networks. Based on that data, you can find the most popular projects and their alternatives.
Ruby Toolbox - Explore and compare open source Ruby libraries
Refined GitHub - Browser extension that makes GitHub cleaner & more powerful