I have used that sometimes and I like it for its simplicity. Want to serve a specific directory quicky?
Want to serve content per cgi/fcgi? Couldn't be easier (but its not as clear documented as I'd like, you need to run it as root I believe, not a problem since it supports privilegue dropping).
cd directory; gatling -S -F -p 1234
I think he wrote gatling mainly as a "real world" usage of his diet libc. (Some slides about the why).
At the moment it seems it isn't working correctly anymore due to not having been updated for a while, probably.
For only one concurrent request at a time it works fine with ~4k requests/second, but with more concurrent requests there are some problems with sockets:
Also, nginx does more requests/second with 1 concurrent request.
socket_error 32 Bad file number
close/writefail 32 98 218
I only tested a small static file with the content "hello world".
On the other hand his website and blog run on gatling very, very reliably so I would guess it's just a problem with new linux behaviour.