Yes, applets can be delivered as jar files. In fact, that's the most common method in which they are deployed. But applets do not use a class having a "main" method like applications do, so they have no Main-Class attribute in the manifest.
To run the applet you'll need an HTML file that contains an <applet> tag, which is described in detail on this page of the Java Tutorial.
It could be as simple as
Ping & DNS - updated with new look and Ping home screen widget