Most engineers create tools, Google is not special in that way. But even when there's a similar open-source tool, it may be difficult to integrate with interna

Most engineers create tools, Google is not special in that way. But even when there's a similar open-source tool, it may be difficult to integrate with internal systems. There's a lot of benefit to a consistent set of technologies (data formats, storage systems, etc) so that's often a reason to write internally. There is a lot of open source software in use at Google so I wouldn't say there's a lot of reinventing the wheel. And when there is an internal clone, the requirements are often necessarily different enough to warrant writing an internal version.