Actually it is known as a LocalDirector and is now classed as an EndOfLife (EOL) Product.

They are Cisco Layer 4-7 switches and are used for Intelligent Server Farm Load Balancing.

The models were the 400 series (417 and 417G).
Have a look at the Cisco Web Site

The LocalDirector has been replaced by the CSS 11500 series switches.

CSS 11500 series switches

The Cisco CSS 11501 Content Services Switch is a compact fixed-configuration platform that delivers rich Layer 4-7 traffic management services for e-business applications. The Cisco CSS 11501 is appropriate for load balancing small web server clusters, supporting eight 10/100 Ethernet ports and one Gigabit Ethernet port though an optional small-form-factor, pluggable gigabit interface converter (SFP GBIC).

For medium- and large- data centers--requiring greater performance, higher port densities, and modularity--customers have the choice of the Cisco CSS 11503, Cisco CSS 11506 and the Content Switching Module for the Cisco Catalyst 6500.

Have a look at the Cisco Web Site