OpenGrok is a source code search and cross-reference engine. It helps programmers to search, cross-reference, and navigate source code trees to aid code comprehension. It can understand various program file formats and version control histories like Monotone, SCCS, RCS, CVS, Subversion, Mercurial, Git, Clearcase, Perforce, and Bazaar. The name comes from the term grok, a jargon term used in computing to mean "profoundly understand." It is mainly written in Java, with some tooling done in Python. It relies on the analysis done by Ctags. There is an official Docker image available.