Vectr is a new, free graphics editor that you can use on your desktop or in your web browser to create simple, clean vector graphics. If you've ever used pretty much any photo-editing or illustration software, you'll already be familiar with the straight-forward interface. The difference to keep in mind is that vector-based drawings are different from pixels; they're more like polygons in a video game and are infinitely scalable. That makes them ideal for designing mockups of webpages and apps, logos, fonts and other illustrations that aren't 'hand-drawn'.
It's pleasingly intuitive. High-end vector graphics editors like Adobe Illustrator have an intimidating learning curve, but Vectr keeps things parsed down enough to be easily understandable without comprising utility. (If you're a professional designer, Vectr is likely too parsed down — but for average people there are more than enough features to get started.) You can save all your work online, share your work with others, and can export to PNG, JPG or SVG file formats.
The software has been in development for two years and has just now come out of beta. Desktop versions are available for Windows, Mac, Linux and Chromebook, and are functionally identical to the web counterpart. It's a pretty useful tool for most people who don't really need all the features of professional design software.