There's a new kid on the block for web application development, and it's called Plack. I'm not going to go into depth on explaining it here, as the website listed previously does a stellar job of that, but I'm going to explain and talk about what got me started on it, and what made me love it.
I've been a pretty avid MovableType fan since I first got it running. It Just Works(tm). I've always ran it under Apache, however, so when I made the big and permanent transition to nginx, I was befuddled as to how to get it to run under my new toy. A kind sir by the name of Jay Shirley recommended I use Plack to get my old love running under nginx. I talked to the creator of this mystical new being, Tatsuhiko Miyagawa on its IRC channel, #plack. We went back and forth for a few iterations until w(h)e got his mt.psgi script (listed here) working so that MT would be okay with new installs.
The result: A mostly working MovableType installation! The only problem is, I have a MT database dump from MySQL that I either A) need to convert the data portion of the dump to something PostgreSQL (what I've converted to for life) will like, or B) suck it up and set up a MySQL instance for this one app. MT itself runs just fine, it's completely my fault that anything on the database side doesn't work. Miyagawa reports that previous installations work just fine with this, so, as I said, I will need to investigate which route I want to take to get this data into a database for MT.
Either way, my experience was fantastic. Plack is really easy to set up. All the work is done for you, and you can still run things under FastCGI (if you're so inclined). It's a great bridge between server software and a web application, so we're not stranded somewhere in between holding on to the connecting ends of a bridge screaming "HOLY FUCK THIS HURTS AND GOD I HOPE IT HOLDS TOGETHER IF WE HAVE TO CHANGE ANYTHING".
Kudos to you miyagawa, I'm pretty sold on using this from here on out for web apps I write in the future (mostly Catalyst based, for which we have Catalyst::Engine::PSGI!)
UPDATE: Here's the configuration I'm using for nginx: http://wiki.catalyzed.org/codesamples/dhoss/placknginxconf
Sounds like really good stuff. Does anyone have any experience using it with Lighttpd?
I'm not really sure, I know lighttpd is a lot easier to get fastcgi stuff going on, and there are hacks to get MT running under lighttpd, which was the main reason I used nginx for this study. It's really a matter of just http proxying to your running plack instance. I should post the config file! :-)