There are hundreds, if not thousands, of content management systems out there today. An exact number is very hard to find as many systems are less known, spinoffs of other systems or custom builds which are hard to distinguish and classify. There are a few lists of content management systems online that give an indication of how many bigger content management systems there are, that seem to be actively developed and maintained. On the wikipedia list of content management systems, there's a total of 170 systems listed. 20 are Software as a service (SaaS) and 28 are proprietary software. The list on wikipedia is by no means an exhaustive list though and more can definitely be found on other lists online. One of which is the amount of CMS' listed on G2.com, where a total of 250 are listed in the Web Content Management Software category.