Good but very basic
It is an abacus. For learning the ropes, it is very handy. Pros You can click-hold the left mouse button and move multiple beads at a time. Have the option to either show the number that the current configuration corresponds to (Practice) or to not show the number (Soroban). The website linked by the "Instructions" button is very handy. Cons It does not support hotkeys, only the mouse moves the beads. The screen is not resizable. No volume control. No easy toggle between Practice/Soroban. Must return to the home screen and click on the other one to switch. Instructions opens in your default web browser, so you'll have to hit the esc button on your keyboard to get to it. No hotkey for hiding the application.