Microsoft Entourage

Microsoft Entourage was email software from Microsoft that offered features for power users, such as hierarchical folders; integration with contact, task, note, and project managers; and the ability to flexibly customize views. While the open source Thunderbird is catching up, especially by its extensibility through "extensions", Entourage still has many features not yet possible with Thunderbird.

One well-developed feature is the integration of Entourage with AppleScript. Mail "Rules" can be added which, when certain conditions are met, will trigger an Applescript. Thus, for example, one could have a script turn up one's computer's speakers (or a remote ringer, such as is possible with the scriptable Indigo home automation software and corresponding hardware) and speak up that one has received mail from so-and-so, etc.