Clustering Software!!!

[Govind.C]

Greetings All,
I am on the look out for a Clustering software.The  functionality I am 
looking for is "Continuity of service" (For example,assume the server 
servicing a client request, goes down midway, the clustering software 
must be able to continue  the work from where it left, either by 
restarting the service or service the request from a different 
server)Any such Clustering software(Freeware)?

Cheers
Govind