PHP stands for Hypertext Preprocessor. PHP originated as a scripting tool that has quickly taken over the internet thanks to its easy learning curve and large developer community. According to one estimate, PHP is installed on over 244 million websites with server support from virtually all major hosts. PHP is also free and boasts a number of frameworks to simplify web development.
Some of the major websites written in PHP include WordPress and Facebook.
ASP.NET was developed by Microsoft to provide developers with an easy scripting tool for building web pages and web applications. It is a successor to ASP (Active Server Pages), another platform pioneered by Microsoft in the mid-90s. You can code ASP.NET using any .NET supported language, which made it especially popular among .NET developers. Microsoft’s early domination of the web browser market with IE was also responsible for increasing the popularity of ASP.NET.
Some of the major websites that use ASP.NET are PlentyOfFish.com and MySpace.