Watcher в Android Market

Watcher (v. 1.0) Разработано Bitorbit

The application follows the presence of text in the URL content and notifies the user if the condition is filled.

Example (watch for new tweets):

URL: some twitter page
Text: -count">current-number-of-tweets<
Interval: 1 day

Take a look at the source code of your favorite web pages to find more use cases!