"Microsoft Proxy Server 2.0 is an extensible firewall and Web cache server that provides Internet security while improving network response time and efficiency."
http://www.microsoft.com/proxy/guide/features.asp?A=2&B=2
Information: http://www.microsoft.com/proxy/
July 5, 2000 -- Microsoft Internet Security and Acceleration (ISA) Server 2000, the successor to Proxy Server 2.0, is an extensible enterprise firewall and Web cache server that integrates with Windows(r) 2000 for policy-based security, acceleration, and management of internetworking.