Electronics
I've played with various electronics since picking it as an after-school club. I started learning using PIC chips and the ICON programming environment, and bought myself a Netduino 2+ (an Arduino-alike running a version of the .net framework) soon after they were released, along with a Raspberry Pi which is currently serving as a WiFi to ethernet adaptor. I've also played with antenna construction - although nothing more complex than a fan dipole with 1:1 current balun. I recently acquired a clock kit from QRPLabs, although I have yet to assemble it. I also use the knowledge I've gained doing this hobby in my current job as a Test Engineer.