Alt + Tab is probably the most used commonly used combination shortcut keys in Windows, it allows users to switch between open application windows, however if you are more of a mouse user, EdgeSwap will allow you to perform Alt + Tab switches with your mouse.
Once you have downloaded EdgeSwap double click on the executable file to launch it (requires no installation), EdgeSwap will create a system tray icon which will monitor for mouse movements.
To use perform Alt + Tab simply move your mouse to the left hand corner of the screen, this will open up the windows application switcher and automatically scroll through it, to open any application move your mouse away from the corner and the application will come into focus.
A few things that you may want to know about, moving the mouse to the corner may automatically start navigating the applications and the speed at which it does it may not always open up the application you want to when you move your mouse away.
EdgeSwap is a good replacement for people who perform most of their work with the mouse, however the software is a bit rough around the edges and may need to be worked upon a bit.