Copas is a dispatcher based on coroutines that can be used for asynchroneous networking. For example TCP or UDP based servers. But it also features timers and client support for http(s), ftp and smtp requests.
I tagged a new version of Copas in its Github repo. The new version has bugfixes and a 5.3 update;
Added: support for Lua 5.3 (no code changes, just rockspec update)
Fixed: yield across c boundary error (by Peter Melnichenko)
Fixed: bug in wrappers for setoption() and shutdown() (reported by Rob Probin)
Download is easiest through;
luarocks install copas