Another nice mention on the app review site Art of the iPhone.

Every good outdoorsman should know how to tie several different kinds of knots. The right knot could save your life someday. Knots 3D will not only show you how to tie knots via an animation, but also explains how the knot is commonly used and allows you to view the knot in a rotating 3D view. The app features 80 different knots.

Another sweet feature is a full-screen view where you can swipe your finger up or down to see the knot slowly built or undone, so you can take learning at your own pace. You can also pinch and reverse pinch to get a close up/farther away view of the knot. You can save favorite knots for fast access.