IBM Has A Nice API Explorer18 Apr 2017
IBM has a pretty cool explorer format for their API catalog, allowing you to search and browse the IBM API catalog by category, and even broken down preview, beta, and live APIs. It looks like there are about 60+ APIs in the catalog so far, with a mix of uses.
Each API has the essential building blocks like getting started, documentation, pricing, and other resources. I don't see any machine readable index like APIs.json or OpenAPI but will keep an eye out. If I have the time I will generate an index for the project after I'm done with some of the other leading cloud and machine learning platforms like AWS and Google.