One of my greatest challenges so far has been to get the Universal Robotics simulator up and running. Not using it, but just installing it. Having never used Linux before it was a challenge to even set it up, when used to automatic Windows installs. However an excellent PDF showing screenshots of the install can be found at the folllowing link and was a distinct improvement on the older instructions.
The trouble was due to my not having extracted the rar file (similar to zip but doesn't look like it, thus the confusion). Once this was done, it was pretty easy.
Now I need to learn to use it!