If everyone got together and uploaded the same firmware to them, have all of them connect to each other, and some way of routing traffic, and then have it put to some use, we could have LED's and buttons and sensors to cross communicate with other arduino's, so you can then control each others lights and have a bit of fun....
for example, if a protocol over UDP was developed, other than the UDP / TCP / IP layers upon layers... just the raw packet here
So to simplify it.
Broadcast UDPPacket(long Who; byte Action,Value,Extended); //IP address
once this data gets sent to an IP address or broadcasted (however you do that over WAN?!)
Byte 1 = 0x0 Byte 2 = 0x1 Byte 3 = 0x0
Some kind of delimiter, CR/LF? whatever, keep it to something like a 5-6 byte payload, to keep it short and quick. if the packet>5bytes, discard it, etc.
basically, a 3 byte packet 0-FF 0-FF, 0-FF
So Let's Switch a light on (TheirIPAddress,0,1,0); //192.168.0.1 //0 meaning Lights //1 meaning On // 0 meaning, nothing
Decimal again (0-255) 0-6, lights 7-12, Signs, Messages, Alerts 13-18, Warnings, Reminders 19-27, sync timers 28-40, Sensor Data Sharing 41-60, Game Packet Data 61-67, Monitoring Power Outages (if the power goes out, and the Arduino is running off a backup battery, it can report your power out, providing your modem too is still running via a UPS or as i did I'm using a voltage regulator and a small Lead Acid battery which powers both the modem and the arduino if the power goes out) 68-90, Control Servos, cameras, and anything else 91 - 100, Advertisers ONLY, and only if people WANT to see these kinds of packets get through (eg, block 91-100) this way we can control content ... ...
EG, 10 people are hosting something as simple as a LDR, a light diode resistor, you know their locations, you can then gather data from other peoples sensors to help aid your own sensors, discover things people could share and setup experiments
Connect a pizeo speaker to pin 9, people could send the packet to make it beep and then have it switch on a light, but i'm yet to think of any serious uses other than to track weather and temperature, maybe barometer, maybe some kind of basic games setup A row of LED's that light up back and forth, when you hit the button it can see which LED is lit up at the time of the button press, time and stats are calculated real time and then compared to the data generated the other end, or have it sent via server..
Scores, real world hardware/software blending in, i'd mount the LED's into my desk and have two buttons i can press, or have multiple LED's on for some kind of quick fire reaction game...
I'm sure i could think of 100 more uses alone given enough time, but it would have to be a community based collaborative effort and i'll gladly help code it but this aint going anywhere if inobody wants to get involved to begin wtith!