Castanet channels are intended as an improvement on Java applets. Although channels are automatically distributed and installed like applets, they appear to users more like applications. Running on a client machine, a Castanet tuner cooperates across the Internet or an intranet with a Castanet tuner running on a server. The result is a mirrored channel of files on the client. But lack of application persistence and high network overhead have restricted developers to using Java mainly for simple animations and small applets.
Tuners install new versions of a channel's files while the current version is running.
For example, a sports scoreboard channel could receive new scores every few minutes. Castanet channels can create and maintain data, such as documents and preferences, and can communicate data, such as usage patterns, back to their servers. Bongo is a visual tool for designing graphical Java applications. It lets developers build applications much like building a presentation in a presentation graphics package. Among the subjects for channels currently linked to Marimba's Web site are interactive comics, games, and puzzles, and databases, news, and sports news.