This site is PACKED with sims and you can choose to run them different ways. You can choose online, full installation, or one at a time. I’ve listed it from this location so you can choose what you want to do. If you look to the left at the menu, you’ll see “Run Our Simulations.” I picked the “Online” option just to browse, but I’m not sure that I wouldn’t rather have it on CD. Anyway, there are all sorts of toys to play with here. You could get lost in it very easily.
PhET-Physics Education Technology