Sourcetrail

Sourcetrail is a free Open-Source source code explorer that provide interactive dependency graphs and support multiple programming languages including C, C++, Java and Python.
History.
The project was started by Eberhard Gräther after an internship at Google where he worked on Google Chrome and consumed a lot of time (1 month) to implement a simple feature that he expected to be done in 1–2 hours. The complexity of understanding large code-bases by new developers was his motivation to develop a tool that help in understanding the consequences of source code modifications.
The project started as a commercial project in 2016 under the name Coati. In November 2019, Sourcetrail was released as open-source software under the GNU General Public License v3.0.
Concept.
Most of programmers time are invested in reading the source code. Therefore, the goal of Sourcetrail is to help the developers to understand the source code and the relationship between different components. Sourcetrail builds a dependency graph after indexing the source code files and provides a graphical overview of the source code.
It is built in an extendable way, so it could be extended to support more programming languages.