The application modules provide call functionality to the system. These applications are then scripted sequentially in the dialplan. For example, a call might come into Asterisk dialplan, which might use one application to answer the call, another to play back a sound prompt from disk, and a third application to allow the caller to leave voice mail in a particular mailbox.

For more information on dialplan applications, see Dialplan Fundamentals.

All application modules have file names that looks like app_xxxxx.so, such as app_voicemail.so.