It is surprisingly trivial to extend Mongrel to suit your own needs. You can write your own commands, request handlers, filters, and quickly configure them as needed. Unlike other systems, though, you don't have to know anything mentioned in this section to use Mongrel. All of this information is "behind the dirty curtain" and only for the very adventurous types who need it.
It's possible to have your first handler up and running in about ten minutes, and fairly extensive plugins can be written within hours or days. It's not as nice as Rails, Nitro, or Camping, where you can create whole applications in days. When you extend Mongrel, you're working at the bare-metal death's edge and have to do more work to keep things straight. The advantage is that you have full control over what happens and you can squeeze even more speed out of the beast.