Cash flow snowball/ tree tool?

[Sean Gallagher]

Does anyone use a tool of some sort to plan out a cash flow tree with rentals?  Sometimes known as a cash flow snowball.  It's easy to draw out but it's not easy when you want to change your numbers since one thing effects the other.

I'm trying to find something where you can put your first rental at the top, type in it's cash flow and keep working your way down as you acquire more properties.  That's the short explanation, of course the more data points to enter the better.