Did you used have a Hyper Key set up using Karabiner and Seil, but upgrading to MacOS 10.12 Sierra ended that dream and now you're kicking yourself? I did, and it drove me crazy for two days. Here's my hack to get a (mostly) working Hyper Key back without downgrading to OS X 10.11 El Capitain:
* This assumes you're using Caps Lock as your Hyper Key.
As of the time of this post, Karabiner-Elements is in beta and you need to manually update/create a ~/.karabiner.d/configuration/karabiner.json file (UPDATE: I'm told it's now ~/.config/karabiner/karabiner.json) with the following JSON:
{ "profiles": [
{
"name": "Default profile",
"selected": true,
"simple_modifications": {
"caps_lock": "f18"
}
}
]
}
This sets your Caps Lock to the F18 key.
* Be sure to launch or restart Karabiner-Elements after you save your changes to the karabiner.json file.