A collection of excellent free resources for demonstrating the various circle theorems:
Tim Devereux has created GeoGebra applets which allow exploration of the circle theorems. You can access each theorem from the menu on the left which includes a useful summary of all the theorems.
From Suffolk Maths there are many GeoGebra applets available including a set for the Circle theorems. The collection includes a PowerPoint with instructions for drawing circles and measuring angles with Geogebra.
From Nrich comes an interactive Geoboard and a selection of problems to introduce circle theorems. As with all Nrich resources teachers’ notes are included. See these on the Subtended Angles problem for example.
Move A, B, C and D by dragging and experiment.
Note the links to the other circle theorem applets and to a set of videos.
Note also the options at the bottom of the screen.