From a user perspective, one of the benefits of progressive webs apps is that they can be truly multi platform, specially if the developing team behind them has taken extra care to make them truly progressive. That means, of course, adapting them to exploit each browser and each platform capabilities, while fail gracefully in those ecosystems that are less able to provide the user the most advanced features.
What Web Can Do Today is a great resource to learn what you can rely on while developing an app that will run on a browser. Surprising things like bluetooth, geolocation, speech recognition and even local notifications and push messages work well in a lot of major and modern browsers. When a features comes with some limitation in an specific major browser, What Web Can Do Today has a useful section that provides further information.
There are also example codes and live demos available for the busy developer, as well as a list of resources such as links to MDN tutorials and references to the specification will all kind of technical details about the feature.
In addition to What Web Can Do Today there is the well known site Can I use. This super useful site provides information about the level of support that all browsers have of each web technology. The site compiles information about a huge list of versions of Internet Explorer, Microsoft Edge, Mozilla Firefox, Google Chrome, Apple Safari, Android Browser, Blackberry Browser, Samsung Internet, Baidu Browser, QQ Browser and so on, as well as the mobile equivalents of all major browsers.
It also provides usage data for you to know if it is worth it to adapt a feature for an specific bunch of browsers, and that data can be accessed on a global level or on a per country level.
This tool comes in handy for instance to check to what extent you can use ServiceWorkers, a basic part of a progressive web app, in Edge, IE or Safari Technology Preview (spoiler: it won’t work. Yet.)
Now that you have all the resources you need to start building your progressive web app, check some real word examples at: Learning from others: how Telegram, FT, RioRun and Barcelona City Council PWA are built.