[japgolly]

There's also ab (Apache Benchmark) which is super simple and can be all you need sometimes.

[js4ever]

Ab support only http 1.0 requests, I recommend wrk instead: https://github.com/wg/wrk

[williamdclt]

And is included in MacOS (as I discovered after trying to install it for 10min).

Simple example (-c is concurrency, -n is total number of requests to make, -H for headers):

    ab -c 20 -n 50000 'https://someurl.com/someendpoint'