Using Webduino, I've made a simple buzzer you can control over the internet. Frequency cap is at 20000 hz. Enter "random" to choose a random value.
BTW, I'm broadcasting it live at UStream from http://www.ustream.tv/channel/webduino-fun. You can play with it at http://internaldrive.info:8080 with the magic of port forwarding. I will be adding features on the go tonight, so suggest them on the chat or in this forum!
Here's the hardware I have: Ethernet shield from NKC Electronics LCD Display with RGB backlight KS0108 LCD display (needs a little re-wiring but may work) Buzzer Parallax RFID reader 3 logic-level MOSFETs 12V battery 12VDC-120VAC power inverter A bunch of LEDs and resistors (including an IR LED somewhere) A lot of breadboarding wire
It's up to YOU. So far it's just an Arduino and a buzzer and will become whatever you want. So get on and suggest ideas, watch me make it and let you control it.