Development of Ember 1.x for Mac was discontinued 2016 — After a short hiatus, work is now underway on Ember 2 for Mac.
Ember 1.8.5 is available to download from here:
The Ember Safari Extension is not supported at this time.
You can use the following license number to activate Ember:
If you want to use Ember we recommend using a local library only. Do not use Dropbox Sync or iCloud.
Mac App Store & iCloud
If you need to download your content from iCloud you'll need to download a copy of Ember from the Mac App Store (as that is the only version that supports iCloud).
Open the Mac App Store and go to the "Purchased" tab, you should be able to find and download Ember from there.
When you launch the Mac App Store version of Ember it will give you the option of using your iCloud Library. Your Mac should download all the images over the next few hours (could be longer depending on library size).