It took me a while, but I figured it out. It's a logic gate simulator.
1.) Mouse wheel selects the type of the cell you want to place.
2.) Control + click places the selected cell
3.) To connect two cells, hold control, right click on source cell and then on destination cell
4.) Switches can be toggled on/off using right click and LED can be used to indicate the output.
The actual simulation seems to work fine, but the UI is buggy and/or unintuitive.