Zannel, a media-rich microblogging service that launched in late 2007, has a new and free iPhone application that puts many of its features on to the popular portable device.
Called CityWatch, the app takes a similar approach to Loopt and Whrrl in allowing you to see and interact with what's going on in your general proximity. It does this by taking each item that's been posted to Zannel and overlaying it onto a map using its geo tag. This also includes items from other networks, like Twitter, Flickr, and eventually any other service that has an open API.
What's neat in Zannel's case is that this activity becomes exploratory and interactive, as you're able to both post and browse through new content in your city or anywhere else in the world. You can also reply to comments in threaded form, just like you can by using the social network on your computer. Eventually users will also be able to sort through all Zannel's content not just by location, but by topic across the entire network.
In my initial run with the application I actually got a little freaked out since the first photo to pop up in my neighborhood was one I had snapped just a few hours before and uploaded to Flickr. I hadn't even plugged in my Flickr credentials, which you can do, along with Twitter to cross-post the Zannel equivalent of "tweets" and vice-versa.
My only qualm with the otherwise very enjoyable application is that it relies a little bit too much on Safari when it comes to making changes in its settings menu. If you want to authorize Twitter or Flickr, you're kicked off the application and into the browser. The same goes for changing notification settings, which if you're signing up for the first time, are automatically set to opt-you in to a text message and e-mail every time another Zannel member: decides to follow you, publishes a comment, sends you a friend request, or replies to one of your messages. All this can be turned off, but it's annoying that it's turned on by default and must be managed outside of the application.
CityWatch by Zannel (App Store link)