Let me get right to the point: I believe that if there is ever contact with Aliens, they will either be so similar to us as to be funny, or be so different from us as to be nearly incomprehensible. A whale doesn't look like a bacteria, which doesn't look like a rose, or a moose or a mushroom or anybody we know. There are so many forms of life it is mind blowing. But Humans are different from all the rest in a special way. We have technology. How can you have a civilization without the knowledge of time and space? Obviously, the Aliens will have clocks and rulers or tape measures. The Aliens are working with the same 100 or so elements that we have; they'll know the Periodic Table of the Elements. If they have technology and build things, what are their knives, drills and saws going to look like? They better look like ours or they're not going to work, and they better be made of steel since oxygen, sulfur or mercury, for example, are not good materials to make a drill out of. If you want to pick up a small object in a tight space, you'll need tweezers. How stylized can Alien tweezers be? Won't they look like our tweezers? How stylized can their cutting edges be? Won't they be sharp to us, also? We assume that life starts on a planet, and so anything that evolves has got to resist gravity all its life. There are two main ways to change the self-powered elevation of a creature on a planet, one being a staircase and the other an inclined plane. It seems natural to think Aliens will also have staircases and inclined ramps. I think it is also safe to assume that any creature has only a limited amount of energy, so Aliens are definitely going to have elevators and escalators to help them along. I have always been amused to see depictions of Aliens as having lobster claws or tentacles or suction cups on their fingers and so on. Have you ever tried to build something with lobster claws or tentacles? The human hand is very.....uh, handy, when you want to do things. I think that Aliens will have opposable thumbs or something similar. And as for just moving forward, their vehicles better have wheels or they're going to have a hard time moving. Glass is a miraculous substance. What kind of scientific progress could we have made without Telescopes and Microscopes? Obviously, the Aliens will have glass and optical devices similar to ours. We can't imagine a modern world without electricity. We can't imagine an Alien world without electricity, either. Obviously, they have short circuits and blown fuses and wires and batteries, just like we do. And don't forget computers, cell phones , and so on..... I guess you see the point by now; there may be hardly a limit to the shape and size of creatures, but when you want creatures to create a civilization, there are many examples of having only a few ways to do something, and using only a few materials. That's why I think that Aliens are going to be so similar to us as to be funny, or else they're going to be incomprehensibly different. Yes, in the future we will have things that seem miraculous to us, but until this utopia arrives, we have to do the best we can with what we've got. And the same thing is true on any other planet at any other time.