1. What is .NET?
.NET - is the Microsoft Web services strategy to connect information, people, systems, and devices through software. Integrated across the Microsoft platform, .NET technology provides the ability to quickly build, deploy, manage, and use connected, security-enhanced solutions with Web services. .NET-connected solutions enable businesses to integrate their systems more rapidly and in a more agile manner and help them realize the promise of information anytime, anywhere, on any device. Reference
2. Which versions of .NET have been released so far?
The final version of the .NET 1.0 SDK & runtime were made publically available on 15 - Jan -2002. At the same time, the final version of Visual Studio.NET was made available to MSDN subscribers.