That would be awesome.
The RTB forums show how many people are using RTB3 at the time. (Currently only RTB3 beta so not many)
I wonder if you could get the server list and then just add up the player count in each server...?
You can use my handy graph: http://forum.returntoblockland.com/graph.phpThe number of servers & players is also shown in the title bar of the join server window.
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