It's web based, and apparently works on android as well (though I haven't tested it.) It allows you to make flow charts for multi-branching stories and it's really easy to use. The only thing I took a minute to find was how to move around if your chart is bigger than your screen-- there's a "mini-map" in the bottom left, where you can pan your view. This also connects straight to your dropbox account/google drive/computer/external drive so it's pretty neat!
Anywho, you can find it here: https://www.draw.io/#
Here's an example of a chart for a game I'm working on (censored, of course!) just so you can see what it does. Like I said, the tool is really easy to use so it only takes a few minutes.
