We use getsandbox for our initial API designs, using their functionality for mocking stateful behaviour rather than just using canned responses.
Getsandbox supports RAML, although as mentioned in the link, the RAML file used during the sandbox creation must be a single file, with no includes
Using the API Designer, we’ve created modular RAML, using libraries, types and traits to avoid repetition as makes sense. However, this causes issues when working with other tools, which more often than not want a single file to work with. I can see there’s a project node-flat-raml that can assist with this - is this the only way to flatten a modular RAML file into a single file?
Are there any other recommended ways of achieving the same? Anything in the platform itself that could achieve this?