A 16 kg kettlebell and a speed rope. I got a MTB two years ago and managed to stay in shape during warm season but I was lacking something for the cold wet weather. When you combine a speed jump rope, a kettlebell and some body weight exercises you pretty much have it covered. I'm actually in better shape in the winter now but still the bike is super fun when the wood roads are dry.
Spaces. Including "Displays have separate Spaces". I kinda knew it was there all the time but never really used it until recently. It fits very nice with the Chrome "People" feature.
I really got into Linux by setting up servers on CentOS back in 2007. Linux, the resources and the community are great and the fact that those servers still run fine today is a testimony to that.
If you would like to get down and set up a server grab a Debian install kit.
The other option would be to get a RaspberryPI and start with that. Tons of resources and much closer to the hardware as a server install. Good if you re into electronics too.
I am a Mac user myself and you will find that the BSD underneath is mostly what Linux works like. They do say that MacOS is the best BSD available :-) So learning Linux will definitely help you to get much more from your Mac as well.
