As more Web traffic comes from mobile devices -- particularly traffic to e-commerce sites -- it's becoming ever more important for businesses to have content that loads onto small screens easily, quickly and effortlessly. To some degree, native mobile apps until now have filled that need, but they have significant limitations. They must be downloaded, and they don't necessarily have all the functionality of full-fledged websites. It's at this juncture that progressive web applications come in. PWAs exist in a space between apps and websites.