Chrome: Many of your favorite sites have their own Chrome extensions that offer offline browsing, powerful searches, or other features. There's a Web App for That is a Chrome extension that, once downloaded, gives suggestions for future extensions based on the sites you visit most often.
Developer Mihai Parparita found himself intrigued by the concept of discovery, how a user finds apps to install. Generally one finds new apps through recommendations, advertisements, or browsing through the Chrome web store. A bit of brainstorming led to an idea for an auto-discovery mechanism.
Along these lines, I thought I would play around with the Chrome Web Store set of apps. Ideally, if one is browsing a web site that has a corresponding app in the store, a page action icon would appear to indicate this, similarly to feed auto-discovery notification. Conveniently, hosted apps have a urls section in their manifest which indicates which URLs they want to include within the app. This seemed like a pretty good proxy for which URLs the app was "about". I extracted the URL patterns for a bunch of apps, cleaned them up a bit, and used that to implement a Chrome extension (source) which shows the aforementioned page action when visiting pages that match a Chrome Web Store entry.
Once I had that working, it seemed like a straightforward extrapolation to use the history API to also match browser history URLs against app data. When launched the extension shows apps that match history entries, sorted by recency (this is also available via the extension's options page). The fact that the app data lives locally means that all this matching can be done without uploading the history to a server, which is preferable from a privacy perspective.
From my use the app works simply and efficiently, but be on guard for extensions that are nothing more than a link to web site in question.
There's a Web App for That is a free extension for the Chrome browser.
There's a (web) app for that site | persistent.info