  We identify and investigate a computational model arising in molecular
computing, social computing and sensor network. The model is made of of
multiple agents who are computationally limited and posses no global
information. The agents may represent nodes in a social network, sensors, or
molecules in a molecular computer. Assuming that each agent is in one of $k$
states, we say that {\em the system computes} $f:[k]^{n} \to [k]$ if all agents
eventually converge to the correct value of $f$. We present number of general
results characterizing the computational power of the mode. We further present
protocols for computing the plurality function with $O(\log k)$ memory and for
approximately counting the number of nodes of a given color with $O(\log \log
n)$ memory, where $n$ is the number of agents in the networks. These results
are tight.

Computational Complexity;Data Structures and Algorithms