Ran into this list by way of Ongig, who surveyed 3700+ companies to determine the top 99 applicant tracking systems by market share as of April 30, 2017.  Go to the original post to view the top 99 providers and view the methodology.  My top 5 observations about this list appear at the bottom of this post.  Here's your top 20 ATS providers by market share (enable pictures or click through if you can't see the chart):

Interesting stuff, right?  Here's my top 5 observations about this list:

1. No one ever got fired for buying Taleo.  They used to say this about IBM back in the day, and it's not really a compliment.  It means that people make a safe choice when they choose Taleo, often times without really digging into their needs.  It's a default for many people in the market, the same folks who are probably still using Internet Explorer.  If you're still using IE, I'm talking about other people, not you.  :)

2. There's a lot of people with some broken ****.  The methodology used by Ongig was the 3700 most active companies in the recruiting space, so there are some high volume recruiting shops using "homegrown" solutions.  Some of those are probably good, most are really bad, and homegrown automatically feels like an ATS with Cheech and Chong as its spokespeople.

3.  Jobvite has done a nice job gaining prominence over the last decade.  The rise of Greenhouse is also impressive.  Shout out to Newton Software for coming in at #20 - a cool solution like Jobvite/Greenhouse.

4.  Bolt-on afterthoughts come in many different flavors - Whatever ADP is calling their many ATS solutions, those are bolt-on's to a larger HRMS play.  Same thing for Workday, people - because I hear that's still not a ready for prime time solution, regardless of the brand.

5. Undervalued - CareerBuilder, who has a nice suite of solutions including an ATS.  

That's my commentary - what do you see?  Hit me in the comments!