Synfig is a powerful, industrial-strength vector-based 2D animation software package, designed from the ground-up for producing feature-film quality 2D animation with fewer people and resources.
...Complex user interface elements can be realized often in few lines of code. Agar is also extensible at the low-level. The low-level API is documented such that modular drivers can be written which enable Agar applications to work seamlessly under many platforms graphics systems without any change at the application level.
The Doodle project aims to provide a language to easily describe
Origami diagrams and produces a ready-to-print document. Doodle will
free creators from diagramming constraints and increase their capability
to share their creations.