Microsoft is releasing Dot Net Framework once in a a year or so, look at following history of Dot Net Framework..
Version Version Number Release Date
1.0 1.0.3705.0 2002-01-05
1.1 1.1.4322.573 2003-04-01
2.0 2.0.50727.42 2005-11-07
3.0 3.0.4506.30 2006-11-06
3.5 3.5.21022.8 2007-11-09
and now its turn of Dot Net Framework 4.0
Why Dot Net Framework 4.0??
More and more companies are adopting Service Oriented Architecture (SOA), (I am not going to explain SOA in this post, and it’s such an overloaded term and requires special dedication to explain)
Service Orientation mainly takes use of WS-* standards to achieve service orientation.
Managing new requirements, developing those requirements is become more complex.
To overcome these difficulties Microsoft has enhanced .Net Framework and Windows Server, new version of Windows Workflow Foundation (WWF); Windows Communication Foundation (WCF) is a part of .Net Framework 4.0 for Windows Server.
These enhanced capabilities codenamed as "Dublin" by Microsoft.
With these release, WWF and WCF, IIS become tightly coupled and is more enhanced.
WWF is become 10 times faster than earlier version. Workflow modeling is enhanced and comes with lots of prebuilt activities.
Now workflow designer is become more easier than earlier one.
Dublin is currently available with only Windows Server.