None of them is a web app. All of them want to provide certain views on their content that are uniquely identified by their URLs. This is especially true for Tw

None of them is a web app. All of them want to provide certain views on their content that are uniquely identified by their URLs. This is especially true for Twitter and Reddit, which both aim to have their views on tweets and threads to be indexed by search engines. Facebook is probably the least clear one, since they put great effort into eliminating discoverability and accessibility from "outside", i.e. without a Facebook account. They're basically the AOL of today, which was a classic application back then that tried to contain a proprietary "web" of stuff in itself, only accessible if you ran their "browser" application, had an account with them and were logged in, and that "AOL Internet" of course had its own search mechanisms, just like Facebook has its own sophisticated search. However, they're not fully closed-up, they just try really hard to nag you into having an account, which is why I'm inclined to still put them in the "website" camp. However, all of these web sites surely contain certain parts that are in itself "web apps" and that are pretty much isolated from the basic parts of the site (albeit possibly interacting with it at well-defined points through APIs). I guess that this is a logical result of the large engineering teams that are working constantly on what is basically the same big website - at some point, in order to scale out further, it just becomes economic and practical to effectively isolate certain features into mostly separated "apps".