Free again for those who missed out last time.
Choose from 87 different knots and see how they're tied in incredible detail. Watch the knot draw itself or use your finger to tie and untie the knot. Its easy to see where the virtual rope goes in and out and around. (Something about a rabbit and a hole and a tree right? ) Zoom in on the knot to get a closer look or flip it around for another perspective. Can your old school knot app do that?!
Android free as well. For those that have seen the light.
https://www.ozbargain.com.au/node/324722
Edit. Beat me to it with description :-)