AI app builders have exploded in 2026 - but they're not all solving the same problem. Some are polished no-code platforms for quick MVPs. Others are full-stack agent environments that write, deploy, and test real code. This guide breaks down 8 of the most popular AI app builders, covering what each one actually does well, where it falls short, and who it's built for - so you can pick the right tool before you're three days into the wrong one.