Interesting, I hadn't seen that package. Gate does look very similar to Throttler, though it isn't very well documented.

The main difference appears to be that Throttler wants to know the total number of jobs up front and so doesn't need to be told that a new job is starting, where Gate more closely follows the WaitGroup concept of incrementing and decrementing the counters manually.

Group is also interesting, but I don't mind running my own error channels and executing my own routines so that I have a little more control.