I've dabbled with virtual theremins and found them to be a good introduction to the instrument. They can replicate the sound reasonably well, though they lack the tactile feedback and subtle control you get with a real theremin. Apps like iTheremin and Theremin I/O are popular choices among enthusiasts. When it comes to technique, it's all about steady and controlled hand movements, much like playing scales on other instruments. They can be a great way to get a feel for the instrument before investing in a physical one. If you're looking to dive deeper, there are some great online tutorials and resources available for learning the nuances of theremin playing.