Digests can be useful for very active lists when subscribers would rather get one message summarizing the day's (or the week's) activity, either because they don't want lots of messages cluttering their mailbox or because they pay by the message; indexes are a LISTSERV extension of this idea, where only information about the day's subjects and authors is sent, along with information on how to retrieve the messages from the archives. Majordomo handles digesting with an optionally-installed digest script, and it treats the digest as a separate list that users can subscribe to (possibly in addition to the regular list); SmartList's digesting works with separate lists, much the same as Majordomo's, except that no additional script needs to be installed; LISTSERV and ListProc do digesting "out of the box" as an option each user can set as he or she chooses (i.e. "SET listname DIGEST").