When we did a puzzle, it was a very different format, but one consideration was to have puzzles to challenge different sorts of creativity. One would be easier to solve if you knew something about music, one would make sense quickly to someone who had done a lot of web design, one was crypto-based, etc. In this particular puzzle, all the steps ran in series, so you had to solve all of them to claim the prize (which was a month of membership), but for your case you could run things separately, maybe have a bunch of different small prizes or rewards.
One thing that occurs to me is that you could, without initially explaining *what* people are doing, have them perform a bunch of transformations on the letters of their own name or twitter handle, eventually ending up with a string of letters and numbers that they punch into some gizmo, and it spits out a personalized something or tweets at them or whatever. Afterward, you reveal that what they just did was convert their name to hex-encoded ASCII, and hey, this stuff really is within the reach of anyone willing to spend a few minutes doing it. :)
-Nate B-
Florencia Edwards  wrote:
>                 We are going to be at a fair with a stand, and we thought, how cool it would be to have a for example, a board strategy game , where people who go to the fair can start sitting in and play. But, we are a makerspace, so we need to show through this game/ puzzle the kind of stuff we do. So it would be cool it was some sort of game a lot of people can play at the same time, but they have to build something, prgoram, connect stuff... Do you now anything like this? Or do you have an idea of what it could be? 
> We are open for proposals and critics
> Cheers                