Justin Deardorff
Justin Deardorff reviewedLunacy Editor 3.0Free Windows app that opens, edits, and stores .sketch files
 RecommendedPros: 

It works on Windows! Opens sketch files, provides CSS and YAML as well as most basic Sketch functionality. Portable version available. FREE

Cons: 

A bit laggy and keyboard shortcuts are not all the same. It's still in beta though. This will only get better.

This is still in the early stages but I like what I see so far! As a product manager constantly working with designers, I can now open design files on PC for quick screen views, exports, etc. If that's your primary need this will be perfect!! If you are looking for a full featured Sketch replacement, it's not there quite yet.

Justin Deardorff has used this product for one day.
Justin, you know how to motivate! Thank you. Quick update: the next release addresses the shortcuts. The release after will bring speed as we'll start to cache the unaffected objects as the bitmaps.