Picombo uses Rack as a backend framework. That means it works with your server and host. Rack provides sessions, cookies and other kinds of Middleware.
Picombo doesn't enforce a database library or ORM system on you. You are free to choose your own, and Picombo won't complain one bit.
Picombo has built in support for caching. Currently supports File based caches, but new drivers are easy to write and use for your specific environment.
Picombo has a simple, powerful and fast routing class that enables you to build advanced routing schemes. Everything from simple key => value routes to regular expressions, to lambdas can be used to define your routes how you want.
Picombo is event driven, which means it's easy to extend and modify. You can add code blocks to standard system events, and create your own events.