Fireflies in the wild synchronize their glowing although there is no leader to give the tempo. Go to http://ncase.me/fireflies/ and read about the fireflies synchronization phenomenon.
Just like fireflies in the wild, you can create program that synchronize blinking between any number of micro:bit! The firefly program uses two pages, page 1 will run when the light is off and page 2 will handle a glow. You will need 3 micro:bit to make the synchronization work!
page 1
In page 1, we add a rule that clears the screen and keeps a dot 
when the page starts.
The clock of the firefly will be held in 
variable X. It starts at 
1 and once it reaches 8, the firefly will glow.
The 
radio receive moves the clock by 1 whenever a neighboring firefly sent a message.
The 
timer rule moves the clock every 
quarter of a second;
The next rule, 
when variable X changed to 8, transitions to 
page 2 when the clock reaches 8.
Since it is possible that we miss the number 8 because the firefly received many radio updates at once,
we add one last rule, a timer every 3s that transitions to page 2.
page 2
A radio message is sent to other firefly so that they can nudge their clock (
).
The variable X is 
set to 1.
All the LEDs are turned on.
A sound is played.
After half a second, we transition back to page 1 to restart the non-glow phase.
improvement ideas
- use a radio group to avoid interference with other users
- remix this technique with other programs to create new synchronized experiences!