Simbrain is a freeware tool for building, running, and analyzing neural-networks (computer simulations of brain circuitry). Simbrain aims to be as visual and easy-to-use as possible. Unique features of Simbrain include its integrated "world component" and its ability to represent a network's state space. Simbrain is written in Java and runs on Windows, Mac OS X, and Linux.

Simbrain combines three interacting components: a neural network, a world, and a set of one or more gauges (representing a brain, an environment, and some portion of the network's state space, respectively). These components can be linked together in various ways, can be started or single-stepped separately or together, and can be modified on the fly as the simulation runs. The result is an integrated simulation of a brain-circuit in an environment with an emphasis on that circuits internal representations and dynamics.