Chyrp is a blogging engine designed to be very lightweight while retaining functionality. It has powerful theme and extension engines, so you can personalize it however you want. The code is well-documented, and it has a very strong structure that's loosely based on the MVC design pattern. Chyrp allows importation from several different blogging engines and uses a system called "feathers", which are basically templates for custom posts.
Arcavias is an e-commerce framework for Web shops, consisting of an e-commerce library, an administration interface, and different frontends. It's a modular stack which offers flexibility and speed. Unlike other Web shops, it's not a monolithic application. Instead, you have a choice between several user frontends, and you can adapt them to your needs or write one of your own.