Most popular variants of the header value (we only show this when there's just a bunch of variants):

A non-standard header used by Microsoft SharePoint and Office applications to communicate the version of server platform. Since it contains a detailed version of the software, it probably shouldn't be advertised on the public Internet.

Reference...

We have seen 49 websites setting the MicrosoftSharePointTeamServices HTTP header and 36 unique values of this header.