The challenges are open to absolutely everyone - infact it's preferred that as many people as possible join.

There are two types of challenge - there is the regularly monthly challenge and there is the lite challenge. The lite challenge tends to be a smaller project than the regular one so that it is less intimidating to new people or those with much less time on their hands. But you can enter whichever you wish.

I have always seen the challenge as a fun way to gain experience mapping things I would never normally consider trying. It encourages people to move outside of their comfort zone. It's not a super competitive thing. And you get good feedback too.