My First Tangrams (Free or $1.99) is a simplified version of a Tangram puzzle. The background is indented to show where the pieces need to go. They are all the right way up.
TanZen HD (Free or $2.99) is a more traditional version of the game. Students have to work hard to rotate and place the pieces in the correct positons to solve the puzzles.
I introduced both apps at the same time and let my year two students decide which one they wanted to explore. It was good that the students had an opportunity to choose the app that best suited their mood and abilities.