As I continued to search for other applications, I was surprised how many applications in the gallery were, to be blunt, rather trivial-simplistic applications that were little more than tests, even some of the Editor's Picks. Let's be realistic here: I want to see sites that are as powerful as Facebook, because if people are creating a site as big and powerful as Facebook, they'll want to know whether Google App Engine is a viable platform to build it on.
Very few of the applications in the gallery struck me as applications that would grow into something with millions of users, and by no means as big as Facebook. I skipped over these, for the most part, because I wanted to see what GAE is really capable of. I wanted to see an application that would push GAE to its limits and see how it fares. (And I do have to wonder why the people at Google, in trying to encourage the use of their engine, would feature such simplistic apps. Are they really trying to sell GAE as something for little tools but not big Web sites?)
But the first item in the Editor's Picks looked like a good one. It's called PackageTrackr (no "e" before the final "r"). The site points out the application is still a beta, so I won't be overly critical of it. However, it's a cool concept. You can enter a tracking number of a package, and optionally specify a carrier or let the site determine the carrier based on the tracking number. (UPS tracking numbers start with 1Z, for example, so there's nothing particularly magical there. But it's a nice feature.) I put in a UPS number for a package I recently received, and the site immediately retrieved the official summary from the UPS site, and on the right side displayed a Google map that has a set of lines drawn on it showing the route the package traveled. That's pretty handy. I like this tool and will likely use it in the future.
In addition, PackageTrackr is pretty fast. There was a slight delay as it drew the map, and it's hard to say exactly why that was since I don't have access to the code itself. But this is a full-featured, nicely built Web site and not just a silly little test app. I don't know how many people were using the site at the same time that I was, but there are some ways to get estimates. Alexa gives it a rather high number, so it probably doesn't yet have a huge number of visitors. However, it was very quick from the short tests I did with it. That said, it's still nowhere near as big as Facebook.
Another application that somebody built that's featured in the Editor's Picks is called Giftag (only one "t"). This is a clever application that lets people create wish lists, much like the wish list feature on Amazon.com. This is clearly a database-driven application in that users can create accounts and then create wish lists of items such as Blu-ray Discs, including images of the items in their wish list. Using a DNS (Domain Name System) lookup, I was able to determine that the site is hosted on Google. Google applications are required to be hosted on Google; however, I checked anyway, since it's theoretically possible to have a site not hosted by Google that doesn't itself run Google App Engine, but does interact with a GAE site. This particular site is indeed hosted by Google, and that includes storing of the images.
The site is pretty easy to use and reminds me of other sites, such as Twitter. Although I've been making comparisons to Facebook, which has a heavy-duty user interface, Twitter is also a good one to consider. While it doesn't have much of a user interface (because it doesn't need one) compared with Facebook or MySpace, it does have a huge amount of power. Now, Giftag isn't likely to be nearly as huge as Twitter, but it does demonstrate similar programming techniques, and the site works quite well.
Incidentally, when you register the site, it also includes an add-on for Firefox and Internet Explorer. This is an interesting use of Google App Engine, because the add-on, while running in your browser, is interacting with the Giftag site. I'm not going to do a full review here of the site and its capabilities due to space limitations, but I do think this is a clever use of GAE.
So far, these sites are interesting. However, what I'd really like to see is an application with thousands of people using it simultaneously, but that will probably have to wait a few more months-or even another year-as GAE picks up steam.