TITLE: Uses of bisimulation outside of computer science.
QUESTION [11 upvotes]: Bisimulation is one of the most important ideas of theoretical computer science. I was wondering whether bisimilarity is used/known outside of computer science/modal logic? I am aware that it corresponds more or less to back and forth techniques from model theory, but are there any other areas where it finds application?
For those not in the know, here is a definition:

Given a labelled transition system $(S,\Lambda,\to)$,
  a bisimulation relation is a binary relation $R$ over $S$ (that is, $R\subseteq S\times S$) such that for all pairs of elements $p,q\in S$ with $(p,q)\in R$, and for all $\alpha\in\Lambda$, we have 

$p\to^\alpha p'$ implies that there is a $q'$ such that $q\to^\alpha q'$ and $(p',q')\in R$, and
symmetrically for $q$, namely, $q\\to^\alpha q'$ implies that there is a $p'$ such that $p\to^\alpha p'$ and $(p',q')\in R$.


Applications collected thus far in answers include:

process equivalence in concurrency theory
model logic: expressiveness characterisations, modal correspondence theory
coinduction, for example in Game Theory
non-well founded set theory
algebraic set theory
geometric topology

REPLY [2 votes]: Bisimularity of graphs arises in geometric topology.  See "Quasi-isometric classification of graph manifold groups" by Behrstock and Neumann.