At the moment, Wikipedia's list of content management systems features 137 unique CMS products. 59 of these are written in PHP.

And that's only the ones that Wikipedia finds 'notable', which means these are the ones that have significant usage or large enough communities to be mentioned. There's at least twice the amount that aren't notable, and if we count all the CMS systems that many web development agencies produce, then there's a whole lot more CMS systems out there.