According to IBM History Flow Visualization
History flow is a tool for visualizing dynamic, evolving documents and the interactions of multiple collaborating authors.
Git-History-Flow is an implementation of the same concept by taking subset of functionality which are suggested by the author(s). The implementation assumes that the subject is tracked by git. The input to the implementation is generated by a script and is fed to the renderer. The logic to generate the input is fairly simple. For a particular file, all the commits are listed from the beginning of the time. Following this, git log is applied on the first commit and git diff is applied for two subsequent commits.
The implementation supports two display modes and two spacing mode. Two display modes are Community Mode and Latest Commit Mode which is nothing more than Community View and Recent Changes View explained in the document