I got a few reports that Copper 1.3 crashes on Yosemite. I am currently investigating the issue. If you cannot run Copper after an update, you can download 1.2.1 from this URL in the meantime from here. Sorry for the inconvenience. I had to make some last minute changes as Apple didn't approve 1.3 in the first place due to some strange macOS Sierra issues. This might have broken Yosemite support? But I am not sure. Just keep a look at Twitter (@appfruits) or this blog.
After so many months of development and waiting for Apple to get the problem resolved we finally managed to get 1.3 finished and uploaded to the Mac App Store. It should work fine from Yosemite to El Capitan. However, it's been hard to get this release done. Of course I did not rest while I waited for Apple to resolve the deploy issues I have been facing. And migrating all those various parts that I developed separately from each other has been a hard task. This might have caused bugs. I tried my best to validate everything works fine. But it's [...]