If you've never heard of Game Builder before, it's pretty much what the name implies: a piece of software that lets you piece together everything from a simple 3D platformer to the "next indie hit" in a sandbox environment. If you're concerned that you might not have the coding skills to create even the most basic games, don't worry.
You can program an enemy slime to move side to side, for example, or make your main character jump when the space button is pressed. It's all fairly simple stuff, and after an initial learning period, it probably won't be long before even less tech-savvy individuals can create their own fun 3D platforming experiences.
Interestingly, if you really want to emulate the experience of game development in a rudimentary way, you can even invite your friends on board to help you create games cooperatively in real-time.