Introducing MacOSX Tigger, the Tiger Apple should have released in the first place. All window shapes match and there are 2 shading options: Unified and Metal.
Since Apple started shipping internal skins in the iLife applications, Iridium doesn’t really provide a Universal UI anymore. Tigger is more of a hack of existing designs than anything else. So, like Chromium, it won’t be publicly available for download.
No support is offered for this download. This link is left here for historical/archival purposes. Use it at your own risk.