They explicitly answer this question in the FAQ (sketchapp.com/support/faq):
Is Sketch available for Windows or Linux?
Due to the technologies and frameworks exclusive to OS X that Sketch has been built upon, regrettably we are not considering supporting Sketch on either of these platforms.
the fact that its a new product and doesn't come with the legacy of their heavyweights might be refreshing from Adobe. The main issue i have with Photoshop and Illustrator is how bloated they became over the years trying to cater for every possible niche.
Is Sketch available for Windows or Linux?
Due to the technologies and frameworks exclusive to OS X that Sketch has been built upon, regrettably we are not considering supporting Sketch on either of these platforms.