Work is progressing to define requirements for API (and HTTP) request rate limiting. Once complete, we would benefit from a high-level survey of applicable software.
Candidates would be any HTTP reverse proxy/router that either incorporates rate-limiter functionality, or is capable of integrating with an external rate limiter, as well as any stand-alone rate-limiter implementations.
Ideally, this survey would include a matrix of some kind that allowed comparisons across notable attributes (licensing, project health/user base, features, etc).
This survey would likely serve as an input for more exhaustive evaluation(s) of any promising candidates, so investigations here can be kept cursory.