The solution files (*.sln) are the things to open. They're for individual modules of the code, as Shasta pointed out. Yes, it's quite massive. The idea is that you don't have to understand the whole thing at once, though, but can work in isolation on one small part at a time. Most of the work up to know has been on the unit testing framework (UnitTestSharp), DNA (Sunweaver) and the math library (Azimuth), which has stuff for linear algebra and polynomial root finding and basic stuff like that. There's skeletons for the other parts (graphics and physics).
If you want to see how the pieces might fit together, you can see a speculative diagram
here.
Also as pointed out, there isn't a DB3 .exe to run, really. Need to get physics and graphics finished before any sort of DB3.exe could be built. I specifically want to avoid work on an actual .exe until the lower subsystems are done to prevent a horse-before-the-cart scenario. There are unit tests to run for each project, along with some test apps to test that specific feature.
So like for graphics, there's a sample app that will become a really simple paint program to let you draw stuff and see how the graphics system handles it, if it can swap out different graphics modules at runtime (XNA to GDI, etc.), and things like that. For physics I'll probably try to create a physics playground app sort of like
Crayon Physics to test out physics scenarios that we're interested in, like towering plants, digging into the ground, etc., to make sure they're stable. For math, there's the starts of a performance analyzer (since linear algebra stuff tends to be quite slow), etc.
If you're looking for a module to work on, someone figuring out graphics would be a pretty good, self contained project. I've sort of made a hash of it so far, but the idea is that it's a vector graphics library with support for hot swapping different ways of doing graphics based on your system. I was starting to play with adding skeletal animation as well, to make it useful for other game projects I might want to work on in the future, but that's right about when I started to dislike how things were going, so I might need to rethink that.
