Ask HN: Can you recommend modeling software?

I'm looking for some advice; I'd like to make collapsible steps in order to more easily enter my attic space. I'm looking for a tool that I can use where I can lay out 2x4s, and place hinges or other screws/nails in the wood and see how the steps might lay/collapse before I actually attempt such a build. Are there tools out there that would allow me to tinker with the design?