Microsoft .NET Framework is an integral Windows component that supports building and running the next generation of applications and Web services. The key components of the .NET Framework are the common language runtime (CLR) and the .NET Framework class library, which includes ADO.NET, ASP.NET, Windows Forms, and Windows Presentation Foundation (WPF). The .NET Framework provides a managed execution environment, simplified development and deployment, and integration with a wide variety of programming languages. 

Microsoft first stable realease and most used version throught out the world is .net framework 2.0. Framework 2.0 has almost all the necessary libraries, tools to achieve high end applications with minimum effort.

.net framework 3.5 has new features like WPF(Windows presentation foundation), WCF (Windows Communication foundation), WWF(Windows workflow foundation). 

New features of .net framwork 3.5

Below are the some of the new features of 3.5 in the following areas.

Ap.net

.net framework 3.5 includes some enhances on the area of  Asp.net and Visual web developer. Microsoft Ajax library is inlcuded to support ajax functionality on asp.net web applications to create rich internet applications preventing too much postbacks on the server. Now asp.net applications can implement WCF based web services that can be consumed from the asp.net web applications. 

While talking with Visual web developer , it now supports intellisense with javascript and microsoft ajax library which will help developers to spend less time while creating rich internet applications. 

Listview and Datapager are new controls added to the asp.net. Listview is a highly customizable control that also supports edit, insert, and delete operations, as well as sorting and paging functionality.

The paging functionality for ListView is provided by a new control called DataPager.  LinqDataSource control is added on the collection of datasource controls to support Linq interface (one of the most important new feature of .net framework 3.5). 

Common Language Runtime

HashSet(T) provides high performance set operations to the .NET Framework. A set is a collection that contains no duplicate elements, and whose elements are in no particular order.

The EventSchemaTraceListener class provides tracing of end-to-end, schema-compliant events. You can use end-to-end tracing for a system that has heterogeneous components that cross thread, AppDomain, process, and computer boundaries. A standardized event schema (see Event Representation for Event Consumers) has been defined to enable tracing across these boundaries. This schema is shared by various tracing technologies, including Windows Vista diagnostics tools such as Event Viewer. The schema also enables the addition of custom, schema-compliant elements.

The EventSchemaTraceListener class is tuned for logging performance with implicit support for lock-free tracing.

Pipes provide interprocess communication between any processes running on the same computer, or on any other Windows computer within a network. The .NET Framework provides access to two types of pipes: anonymous pipes and named pipes. 

Garbage Collection

The GCSettings class has a new LatencyMode property that you can use to adjust the time that the garbage collector intrudes in your application. You set this property to one of the values of the new GCLatencyMode enumeration.

The GC class has a new Collect(Int32, GCCollectionMode) method overload that you can use to adjust the behavior for a forced garbage collection. For example, you can use this overload to specify that the garbage collector should determine whether the current time is optimal to reclaim objects. This overload takes a value from the new GCCollectionMode enumeration.

Assemblies that run with partial trust can now emit code and execute it. Emitted code that calls only public types and methods needs no permissions beyond the permissions demanded by the types and methods that are accessed. The new DynamicMethod(String, Type, Type[]) constructor makes it easy to emit such code.

When emitted code needs to access private data, the new DynamicMethod(String, Type, Type[], Boolean) constructor allows restricted access. The host must grant ReflectionPermission with the new RestrictedMemberAccess flag to enable this feature, which gives emitted code the ability to access private data only for types and methods in assemblies with equal or lesser trust levels. 

For reflection, a host grant of RestrictedMemberAccess similarly allows restricted use of methods that access private properties, call private methods, and so on, but only for target assemblies with equal or lesser trust levels.

Threading

The new ReaderWriterLockSlim class provides performance that is significantly better than ReaderWriterLock, and comparable with the lock statement (SyncLock in Visual Basic). Transitions between lock states have been simplified to make programming easier and to reduce the chances of deadlocks. The new class supports recursion to simplify migration from lock and from ReaderWriterLock.

Throughput for the dispatch of work items and I/O tasks in the managed thread pool is significantly improved. Dispatch is now handled in managed code, without transitions to unmanaged code and with fewer locks. The use of ThreadPool is recommended over application-specific thread pool implementations.

Time Zone Improvements

Two new types, DateTimeOffset and TimeZoneInfo, improve support for time zones and make it easier to develop applications that work with dates and times in different time zones. For a discussion of which type to use in particular situations, see Choosing Between DateTime, DateTimeOffset, and TimeZoneInfo.

The new TimeZoneInfo class largely supplants the existing TimeZone class. You can use TimeZoneInfo to retrieve any time zone defined in the registry, rather than just the local time zone and Coordinated Universal Time (UTC). You can also use this class to define custom time zones, to serialize and deserialize custom time zone data, and to convert times between time zones. For more information about developing applications that use the TimeZoneInfo class, see Times and Time Zones.

The new DateTimeOffset structure extends the DateTime structure to make working with times across time zones easier. The DateTimeOffset structure stores date and time information as a UTC date and time together with an offset value that indicates how much the time differs from UTC. 

Networking:

The Socket class has been enhanced for use by applications that use asynchronous network I/O to achieve the highest performance. New classes have been added as part of a set of enhancements to the Socket namespace. These classes provide an alternative asynchronous pattern that can be used by specialized high-performance socket applications. These enhancements were specifically designed for network server applications that require the high-performance.  

Windows communication Foundation

Windows Communication Foundation (WCF) is Microsoft’s unified programming model for building service-oriented applications. It enables windows programmers to build secure, reliable, transacted applications that integrate across platforms and interoperate with existing systems.

Windows Presentation Foundation

The Windows Presentation Foundation (or WPF), formerly code-named Avalon, is a graphical subsystem in .NET Framework 3.0. WPF  uses a markup language, called XAML, for rich user interface development.

 It provides a consistent programming model for building applications and provides a clear separation between the user interface and the business logic. A WPF application can be deployed on the desktop or hosted in a web browser. It also enables rich control, design, and development of the visual aspects of Windows programs. 

WPF will be used for futrue microsoft applications. The code editor in Visual Studio 2010 has been rebuilt on WPF. WPF makes lot easier if you plan to built rich interactive application which also consists of UI animation. 

Microsoft Silverlight objects can be created using WPF that can be embedded on the web applications to interactive with user and data. 

Some intresting Features of wpf

• Supports vector-based graphics, which allows scaling without quality loss.
• Supports 3D model rendering and interaction in 2D applications.
• Interactive 2D content can be overlaid on 3D surfaces.
• WPF provides shape primitives for 2D graphics along with a built-in set of brushes, pens, geometries, and transforms.
• WPF supports the video formats WMV, MPEG and some AVI files by default, but since it is Windows Media Player running beneath, WPF can use all the codecs installed for it.
• WPF supports time-based animations, in contrast to the frame-based approach. 
• WPF has a built-in set of data services to enable application developers to bind and manipulate data within applications. 
• A set of built-in controls is provided as part of WPF, containing items such as button, menu, grids and list box.
• A powerful concept in the WPF is the logical separation of a control from its appearance. A control's template can be overridden to completely change its visual appearance.
• WPF provides for BitmapEffects, which are raster effects applied to a Visual. 

Windows Expression Blend tool is a powerfull tool to work with WPF. Visual studio 2008 also supports creating, editing and building wpf applications.