Glassdoor seems like a pretty simple website, but it's still the main platform for company salaries and reviews. That data allows them to get a piece of the huge recruiting market. Compare to LinkedIn which is 20x more expensive.
Not just recruiting, but evaluation and screening as well. Most people here are probably only looking for high-paying white collar jobs but Indeed does a huge business in front-line and blue collar postings. Now they're offering screening between application and in-person interviews and can take care of a lot of the filtering work that used to mean a huge pile of resumes. I see the GD purchase as breadth while they're also moving up & down the HR pipeline simultaneously.
Recruit is kind of a funny setup - itself it's not that large (I think around 800 people) but it owns/controls companies totaling tens of thousands of employees worldwide.
