https://eyewire.org/explore

Eyewire is a game to map the brain from Sebastian Seung's Lab at Princeton University. This citizen science human-based computation game challenges players to map retinal neurons. Eyewire launched on December 10, 2012. Over five years, 250,000 people from 150 countries have signed up.
 
Eyewire challenges players, "Eyewirers", to map neurons in 3D. Upon registering, players are directed through a tutorial that explains the game. Supplementary video tutorials are available on the Eyewire Blog.

In Eyewire, the player is given a cube with a partially reconstructed neuron branch stretching through it. On the right side of the screen is a grayscale image of the cross sections of neurons. The player learns to "color" inside a gray outline of a single neuron branch, which usually extends from one side of the cube to another. As a player colors, segmentations that were generated by AI are added to the 3D section on the left of the screen. Reconstructions are compared across players as each cube is submitted, yielding a consensus reconstruction that is later checked by expert players of rank Scout and Scythe. These players have the power to extend branches, remove erroneous segments (nicknamed "mergers"), and flag cubes for further review. This end result is volumetric reconstructions of complete neurons.