It's a lot like OpenResty (https://openresty.org/en/), which is Nginx with a Lua interpreter embedded and bridged to its request-response cycle (the OpenResty page explains the point of that pretty well); but instead of Lua, Unit has a bunch of other language runtimes embedded.
I haven't found any embedded interpreters or runtimes here. Quite the opposite, I see they have libraries they ship with other languages that a user has to use in order to receive http requests.
Why remove Lua, though? I'm a heavy Lua user, which is why I use the openresty bundle of nginx. There's no reason for me to try this out. This is unfortunate!
