There is a solution!
Copied from a reddit post:
Hey there,
Brackets is not dead! The only problem on current installations is a broken extension manager functionality. A direct, transparent transfer of the registry to the new domain wasn't possible because of Adobe's implementation of SSL. A quick fix for this is simple, we just have to edit config.json:
Locate your Brackets installation in your filesystem
Go to /www/config.json and open it up to edit
Find this: "extension_registry": "https://s3.amazonaws.com/extend.brackets/registry.json",
Change to: "extension_registry": "http://registry.brackets.s3.amazonaws.com/registry.json",
Find this: "extension_url": "https://s3.amazonaws.com/extend.brackets/{0}/{0}-{1}.zip",
Change to: "extension_url": "http://registry.brackets.s3.amazonaws.com/{0}-{1}.zip",
Save and (re)start Brackets, the extension manager should work again
I welcome you to see more comments there in the original post.
for my Mac, it was simply this command in the terminal to open the config:
open /Applications/Brackets.app/Contents/www/config.json -a Brackets