GitHub Visualizer - Enter user/repo and see the project visually
SonarQube - SonarQube, a core component of the Sonar solution, is an open source, self-managed tool that systematically helps developers and organizations deliver Clean Code.
Gource - Gource is a software version control visualization tool.
Sourcetrail - Sourcetrail is a cross-platform source explorer for C/C++ and Java.
SyntaxDB - Easily look up programming syntax for multiple languages
ProjectCodeMeter - Measures Software Development Productivity, Estimates Costs, Source Code Metrics and Quality using Automatic Analysis