Ask HN: Sketch alternatives for Linux and Windows

Sketch has received a lot of attention on here - and in our designer communities - over the last 6-8 months. As vectors are now established as a design trend, I want to start drawing my own quickly and easily. So far I have been depending on Noun Project, and other fantastic resources. Can anyone point in the right direction of a Sketch alternative for Linux (and Windows), so I can start to get my hands dirty? BONUS: Are there any top-quality tutorial/essential reading for getting started?