User interface design: There are many things which the user interface still needs. Handling of unsaved documents: what to do on startup? Examining ways to streamline the user's workflow. Improve the way tracks behave when components are dragged around.

High performance code to enforce design rules: This will probably need a combination of good space partitioning, and taking advantage of the GPU, perhaps using something like The Brook Language, GPGPU at Sourceforge. There are also resources at http://www.gpgpu.org/ and Dominik Göddeke -- GPGPU.

Totally free-direction autorouter: This will be a different from traditional autorouting, because tracks can go in any direction, and can also be sequeezed between other tracks.

Parametric 2D sketching interface and algorithms: If you have used a modern 3D Solid CAD package (like Solidworks), you'll know what I mean.

This will be important for specifying the outline of the board, and for correct placement of components.

Get it to compile on Linux and Mac:

General software advice: I'd love someone to take a look at the code, and help me get it to a point where it can flourish in an open-source community.