The parametric speaker is a highly directional speaker which projects sound in a narrow beam, much like a flashlight. Sound coming from the speaker can then be pointed at individual people and has found uses in public advertisements and military defense. The extra cool think about this speaker is that it actually only sends out high-frequency ultrasound which we can’t even hear, but the air reacts to the ultrasound nonlinearly and generates audible frequencies right at our ears. For more information, see the TED talk: http://www.ted.com/talks/woody_norris_invents_amazing_things?language=en
The Theremin is an instrument which can be played without touching it. The frequency varies depending on how close to the antenna your hand is, and it can be a very difficult instrument to play well. It was once used to make sound effects for sci-fi movies in the 50’s but it has also seen some talented musicians pick it up and make some music with it: http://www.ted.com/talks/pamelia_kurstin_plays_the_theremin?language=en
Effect pedals are sound-modifying devices which can add distortion, delay, phasing, echo, chorus and many other audio effects to an electrical audio signal such as the one coming from an electric guitar, violin or keyboard. There are numerous demos of different pedal styles online: https://www.youtube.com/watch?v=HANs086-6AU
Atari Punk Console
The Atari punk console is the name given to a chiptune-like synthesizer which makes a bunch of crazy noises depending on the positions of the knobs. Like the Theremin, it can be difficult to master and make decent music, but still is a fun and easy synth to build.