Apple Developer Apps & Services
There are no other paid apps given away for free to members.

However, you should be aware that various services/features of the developer membership such as support requests and the ability to generate secure certificates, are things that would otherwise cost money.

https://developer.apple.com/programs/whats-included/

In terms of other perks: beta software releases (well, earlier than the public) and developer account tools. macOS Server would count as either/both of those depending on when you visit the member download page.