It is an internally built versioning tool with similar interface as perforce https://cacm.acm.org/magazines/2016/7/204032-why-google-stor...

Google uses Piper, that is vaguely inspired by Perforce workflow, but significantly less confusing.

Source: https://cacm.acm.org/magazines/2016/7/204032-why-google-stor...

> CL: Stands for “changelist,” which means one self-contained change that has been submitted to version control or which is undergoing code review. Other organizations often call this a “change” or a “patch.”

source: https://google.github.io/eng-practices/

Perforce isn't confusing if you take the time to learn it and understand its model. It even does certain things better than git if you ask me:

• You can make a "branch" of portions of a codebase and have it appear side by side with the original. You don't have to keep doing `git checkout` to switch between your version and the original.

• Renames and copies are actually remembered and recorded, instead of haphazardly reconstructed after the fact using heuristics.

• Have multiple pending CLs. Sort of like having multiple independent WIP commits at the same time. It's quite powerful when you need to do two different things and more convenient than `git add -p` to select hunks.

think "PR"