Creatures Evolution Engine
The Creatures Evolution Engine is the name given to the game engine used by Creatures Adventures, Creatures Playground, Creatures 3, Docking Station and Amazing Virtual Sea-Monkeys. It is also referred to as c2e, which is the internal Creature Labs name for the engine (which, according to Lisa de Araujo, stands for 'creatures 2 enhanced').
It was almost a complete rewrite, built using C++ and the STL, and written in a portable manner (it was eventually ported to Linux and Mac OS X) as opposed to the Windows-centric design of the previous engines.
There is an open-source 'clone' of the Creatures Evolution Engine called openc2e.