New instance of the platform game builder is now up and running at runjumpbuild.com.
I've set it to report errors on login failure, so if your login is rejected, could you please mail me with the error message? It will help me debug whatever the problem is that keeps people from logging in.
I have made the physics constants (gravity, friction, acceleration, jump power, and max speed) editable in the level editor. So you can make the low-grav moon level or the low-friction ice level or whatever. If you tweak these numbers and come up with something you think is better than the default set in terms of the feeling of control over the character, let me know and I can make it the new default set!
Oh, and if you're tired of being a sticklyman, try setting your avatar image URL to elf.png or running_petunia_frames.png. You can also set the tileset URL to tileset.png which will apply some textures to the platforms and trinkets.