In a nutshell, it lets you paint halftones, line and crosshatching with the blob brush tool.
Check out this video and prepare to have your mind blow (the audio is not super great but it makes up for it when you see what the product does).
Here's a little fun fact: These halftones and lines were built using a 1940s Army surplus catalog that I paid $200 for in a bidding war on eBay. But I don't regret it for a second because these textures are AWESOME!
P.S. Due to the hugely successful nature of VectorTone we've made a whole set of different brushes inspired by historical material. Brushes like ink and water, sponge brushes, charcoal, pencils and chalk. It's called The Vector Brush Toolbox and it's awesome. Plus when you buy the entire bundle you save mucho moola!