I'm studying the area of IDPs and was happy to stumble on https://internaldeveloperplatform.org/ It was specifically refreshing to see they also promote solutions where the IDP is a hosted service and not an in-house set up (so "internal" but "external"...) Some very good resources there and a good range of solutions from Coherence to Platform.sh - different approaches but in many cases similar objectives and result - make life easier for developers when setting up new preview environments and production projects.

Bunnyshell.com also