Clarification about Operational Support System
The Wikipedia definition of Operational Support System (OSS) makes it sound like a term of art from telecommunication companies.  I haven't seen this come up in systems administration over many years of working in this area.  The top vendors in the OSS space are Ericsson, Nokia, and Huawei.  I never see those guys trying to help me manage cloud deployments, so I don't feel there's much overlap with what Ansible Tower does.
Ansible Tower provides a GUI for working with the anisble configuration management tool.  While this provides similar functionality to what it seems an Operational Support System to be, I doubt Ansible Tower is being used as an OSS by anyone.  It wasn't mentioned in any of the product comparisons I googled for OSS vendors.
Tools similar to Ansible Tower would be in categories like deployment tools or infrastructure visualization.  A few examples of these:

rundeck
DeployHub
Foreman

There's also overlap with CI/CD tools.