There are many different styles of question which can be used very effectively to develop knowledge of mathematics and mathematical skill.
General use of interactive elements
A very simple tool is to allow the dragging of cards around on the screen. This device can be used in many ways.
IFFY logic - This exercise gives practice in logical reasoning
Proof sorters - Proof sorters give students access to proofs beyond their means to construct directly, and can be used to transmit many mathematical ideas
Fluency and practice
There are many bad examples of this sort of thing on the web. Rather than simply use multiple choice, there are better ways to develop speed and fluency.
Sometimes lots of small questions build up into a nice collection of structured exercises. These are good for allowing exploration of breaking down a difficult concept into more manageable chunks
Problems which can be solved in many different ways
The same problems can often be solved in many different ways. This allows students to revisit problems when new content is learned.
Curved Square
Problems which may be used in multiple ways
The same problem can be used by a teacher in multiple ways, depending on the needs of the students.
Problems allowing exposure to advanced mathematics
Often problems can be created which give access to the ideas involved in advanced mathematics, without the need for being able to do the advanced mathematics