It's CMSes and OSes. You're looking for the plurals, so you definitely don't need to use a possessive apostrophe there because there's no ownership in the sentence.

Also, because they're acronyms you pronounce by enunciating the words, my instinct would be to use OS's (as you would pronounce the 's, O-S-es). But that's up for debate.

For example:

The OS's kernel blew up (possessive apostrophe, the OS owns the kernel)

He had a wide range of OSes to choose from (pluralization, there are many OSes)