It’s designed for kids, but the it’s not too hard for adults! Basically, letters fly by slowly on a clothesline, and you have to press the correct letter on your keyboard before they cross to the other side. It assumes you know the letters, i.e. it doesn’t teach you that a letter is an GIMEL or a DALET, but just requires you to type that letter on the keyboard.
It’s free, runs on the web, but does require a free copy of Java to be installed (if you don’t already have it installed).