Swoosh

Swoosh allows you to mute an incoming call with a swoop.
Just pass your hand above the screen when your phone rings to mute the ringer.

Swoosh uses the proximity sensor of your device (the one that turns off the screen when you put the phone to your ear during a call) as a trigger for muting an incoming call.
When a call comes in, pass your hand above the screen (not too far away though, no more then an inch or two) or more precisely, above the proximity sensor, which is usually located at the top edge of the screen, and - MAGIC - the call is muted!

Pocket mode!
With Pocket mode enabled, an incoming call is automatically muted when you take the device out of your pocket / bag / pouch / etc. or in case the device is laying face-down on any object (i.e. table) and you pick it up during an incoming call.
In order to enable Pocket mode, just click on the Swoosh icon and check the Pocket mode check-box.

If you are having difficulties to make it work, don't leave bad reviews. Contact me and I'll do my best to assist.