Difference between .NET 2.0/3.0/3.5 Framework

NET framework 2.0:

It brings a lot of evolution in class of the framework and refactor control including the support of

Generics
Anonymous methods
Partial class
Nullable type
The new API gives a fine grain control on the behavior of the runtime with regards to multithreading, memory allocation, assembly loading and more
Full 64-bit support for both the x64 and the IA64 hardware platforms
New personalization features for ASP.NET, such as support for themes, skins and webparts.
.NET Micro Framework


.NET framework 3.0:

Also called WinFX,includes a new set of managed code APIs that are an integral part of Windows Vista and Windows Server 2008 operating systems and provides

Windows Communication Foundation (WCF), formerly called Indigo; a service-oriented messaging system which allows programs to interoperate locally or remotely similar to web services.
Windows Presentation Foundation (WPF), formerly called Avalon; a new user interface subsystem and API based on XML and vector graphics, which uses 3D computer graphics hardware and Direct3D technologies.
Windows Workflow Foundation (WF) allows for building of task automation and integrated transactions using workflows.
Windows CardSpace, formerly called InfoCard; a software component which securely stores a person's digital identities and provides a unified interface for choosing the identity for a particular transaction, such as logging in to a website


.NET framework 3.5:

It implement Linq evolution in language. So we have the folowing evolution in class:

Linq for SQL, XML, Dataset, Object
Addin system
p2p base class
Active directory
ASP.NET Ajax
Anonymous types with static type inference
Paging support for ADO.NET
ADO.NET synchronization API to synchronize local caches and server side datastores
Asynchronous network I/O API
Support for HTTP pipelining and syndication feeds.
New System.CodeDom namespace. 

Difference between .Net 4.0 and .Net 3.5, 2.0

.Net Framework 4.0 comes up with some of major changes as compare to previous versions of .Net Framework 3.5 and 2.0

Following are list of Major Changes in .Net 4.0

• ControlRenderingCompatabilityVersion Setting in the Web.config File 
• ClientIDMode Changes 
• HtmlEncode and UrlEncode Now Encode Single Quotation Marks 
• ASP.NET Page (.aspx) Parser is Stricter 
• Browser Definition Files Updated 
• System.Web.Mobile.dll Removed from Root Web Configuration File 
• ASP.NET Request Validation 
• Default Hashing Algorithm Is Now HMACSHA256 
• Configuration Errors Related to New ASP.NET 4 Root Configuration 
• ASP.NET 4 Child Applications Fail to Start When Under ASP.NET 2.0 or ASP.NET 3.5 Applications 
• ASP.NET 4 Web Sites Fail to Start on Computers Where SharePoint Is Installed 
• The HttpRequest.FilePath Property No Longer Includes PathInfo Values 
• ASP.NET 2.0 Applications Might Generate HttpException Errors that Reference eurl.axd 
• Event Handlers Might Not Be Not Raised in a Default Document in IIS 7 or IIS 7.5 Integrated Mode Changes to the ASP.NET Code Access Security (CAS) Implementation 
• MembershipUser and Other Types in the System.Web.Security Namespace Have Been Moved 
• Output Caching Changes to Vary * HTTP Header 
• System.Web.Security Types for Passport are Obsolete 
• The MenuItem.PopOutImageUrl Property Fails to Render an Image in ASP.NET 4 
• Menu.StaticPopOutImageUrl and Menu.DynamicPopOutImageUrl Fail to Render Images When Paths Contain Backslashes