Try Obby Maker free in your browser, with nothing to install and no account. Build an obstacle course and make it yours. Snap together platforms, lava, spinners, sliders, bounce pads and ladders, then open any piece and change the program inside it: lava is one line, and changing that line makes a trampoline. Give a stage its own rules (moon gravity, rising lava, lights out), let a loop build a spiral staircase, then publish the course and race the ghosts of everyone who has finished it.