At this time there are no available builds for download. If you want to see Chimera in action, you'll have to bite the bullet and build it yourself.
Follow all of the instructions here for building Cocoazilla and CocoaEmbed. Although you don't technically have to build CocoaEmbed, you do have to use Project Builder to build the NSBrowserView framework in mozilla/embedding/browser/cocoa.
Once you have a Cocoazilla build, you should then pull the chimera files. You should check out from the directory above your mozilla source tree, so that you end up with chimera as a sibling directory of mozilla.
You should then open up the chimera project in Project Builder and build it. It will handle copying all of the files that it needs out of the mozilla source tree and will produce a complete Chimera.app that you can then run.
Be patient with the build process. You may find that CocoaZilla is on the floor from time to time (or that Chimera is on the floor even though CocoaZilla builds). We'll do our best to keep the Chimera side of things operational, but we can't guarantee stability in the mozilla source tree.
If you have questions about building, use the chimera mailing list or hop on to #mozilla, and someone can help you out.