Cisco IronPort AsyncOS

слухи слухами, но правда куда интереснее - АсинкОСЬ это БСД + 3 свистелкопирделки.

Developing the Cisco IronPort AsyncOS Operating System

Cisco started with a FreeBSD kernel and made three major changes to create the Cisco IronPort appliance:

Developing a stackless threading model that allows the appliance to support more than 10,000 simultaneous connections, rather than the 100 connections of a traditional operating system.
Creating a high-performance file system and an I/O-driven scheduler optimized for the asynchronous nature of messaging (hence the name AsyncOS).
Designing the Cisco IronPort AsyncOS operating system to have no user-accessible UNIX shell. This makes the system highly secure and much simpler to administer. Users interact with a web-based GUI or fully scriptable command-line interface.

The Cisco IronPort AsyncOS operating system lets Cisco IronPort appliances process mail more than 10 times more efficiently than traditional UNIX systems do, providing extremely high capacity and availability.