Windows Presentation Foundation

In the earlier GUI frameworks, there was no real separation between how an application looks like and how it behaved. Both GUI and behavior was created in the same language, e.g. C# or VB.Net which would require more effort from the developer to implement both UI and behavior associated with it.

In WPF, UI elements are designed in XAML while behaviors can be implemented in procedural languages such C# and VB.Net. So it very easy to separate behavior from the designer code.With XAML, the programmers can work in parallel with the designers. The separation between a GUI and its behavior can allow us to easily change the look of a control by using styles and templates.

Web API as the name suggests, is an API over the web which can be accessed using HTTP protocol. It is a concept and not a technology. We can build Web API using different technologies such as Java, .NET etc. For example, Twitter's REST APIs provide programmatic access to read and write data using which we can integrate twitter's capabilities into our own application.