Though they are separate products with different UIs and features, Teams, Skype consumer version, and (maybe?) Microsoft-hosted Skype for Business all run on the same communications tech stack, made by Microsoft's Intelligent Conversation and Communications Cloud division.*

Interestingly, it looks like Teams was at one point code-named "Skype Spaces" - a name which occasionally appears in Teams deep link URLs.

* see this job ad here: https://careers.microsoft.com/us/en/job/834482/Site-Reliabil...