How to fix Sierra not remembering SSH keys.
As described in detail on https://openradar.appspot.com/27348363, macOS/OS X till Yosemite used to remember SSH keys added by command ssh-add -K .
Unfortunately this way no longer works and command ssh-add -K in macOS Sierra no longer saves SSH keys in OS's keychain. As Apple Developer stated: "That’s expected. We re-aligned our behavior with the mainstream OpenSSH in this area."
SelfControl is a free and open-source application for Mac OS X (10.5 or above) that lets you block your own access to distracting websites, your mail servers, or anything else on the Internet. Just set a period of time to block for, add sites to your blacklist, and click "Start." Until that timer expires, you will be unable to access those sites--even if you restart your computer or delete the application.
"The MacPorts Project is an open-source community initiative to design an easy-to-use system for compiling, installing, and upgrading either command-line, X11 or Aqua based open-source software on the Mac OS X operating system."
Some very useful utilities. Service Scrubber helps you manage OS X services, Witch turns command+tab into something that can access the windows of individual applications, not just the applications themselves.