mimestream (a native gmail client) is a relatively new app and is fantastic. still in beta, but actively developed and solved the one thing I wanted more than anything... to be able to command-tab into my email box.
I totally agree about mimestream. It's everything I want in an app -- single focus, Mac-native, fast, and works well.
Two other Mac-native tools that I really enjoy using every day: GitUp (http://www.gitup.co/) and Postico (https://eggerapps.at/postico/).
It works together very well with Secretive[1] which allows you to keep your SSH key in your Mac’s Secure Enclave and require Touch ID to use them, as well as displaying a notification showing what’s trying to access keys. It can also store keys in hardware dongles (like YubiKeys) and has a nice native UI for managing multiple keys.
[0]: https://git-fork.com/ [1]: https://github.com/maxgoedjen/secretive