Pure exchange economy: Given an initial endowment are multiple equilibria possible?
Yes. The Debreu version of the Sonnenschein-Mantel-Debreu theorem guarantees that excess demand has to satisfy very little restrictions if there are as many consumers as commodities.

An explicit example of multiple equilibria in a $2\times 2$-exchange economy can be found in


  Shapley, L. S., and M. Shubik. “An Example of a Trading Economy with
  Three Competitive Equilibria.” Journal of Political Economy, vol.
  85, no. 4, 1977, pp. 873–875.


In the example, both consumers have even quasi-linear preferences, which are (necessarily for nonuniqueness) linear in different commodities.