Today, app servers are mostly separated from front-end servers because, it turns out, it's best to not hold on to too much memory and/or threads while waiting f

Today, app servers are mostly separated from front-end servers because, it turns out, it's best to not hold on to too much memory and/or threads while waiting for a slow client to receive their stuff. So async servers like Nginx are used on the front tier and they knock to app servers over the net. But Nginx does have a Lua module, and, I think, Perl. Afaik both are in the free version. Mostly used to augment configuration, or for lightweight interfacing directly with databases (ahem Redis and Memcached cough).