How to map right Alt to Context-Menu key

You can use Autohotkey.

When you Launch Autohotkey, it will asks you the following:

To help you get started, would you like to create a sample script in the My Documents folder?

Press YES to create and display the sample script.

This will create a AutoHotkey.ahk file in your Documents Folder. Open AutoHotkey.ahk with notepad and add the following to the end of the file.

RAlt::Appskey

Now run the script by opening the AutoHotkey.ahk file with the Autohotkey application you installed before.

Now when you press the right Alt key you will see the ContextMenu.