Wireless microphones give you the freedom to move around while amplifying your voice, but they can be incredibly expensive. With a Raspberry Pi, a few cheap components and a radio, you can create one for a lot less.
This build from Instructables user taifur transmits what you say into the makeshift lapel microphone over FM radio. Once you have the Pi all set up, you'll be able to amplify your voice with any all-in-one radio or boombox.
This could be useful for giving lectures or presentations where it might be hard to hear you and there isn't a professional PA system. You could also use it in a van or other large vehicle to communicate over the car's speakers. You can find the full component list, necessary code, and step-by-step instructions at the link below.
Raspberry Pi Based Wireless Microphone [Instructables]