So you are a fan of the game Overwatch and would like to build your own Tracer Guns? fntsmn has shared a project that shows you how to do just that. This Tracer Gun has Adafruit electronic components and LEDs that can be controlled from an iPhone. The design was done using Rhino 3D.
The above GIF shows how these pistols look. You can find out more about this project on Instructables.