I created a new section for challenges and contests.http://www.uglyhedgehog.com/s-25-1.html
This new section will be included in the digest, right after the Main section, and it will be shown to all users. This way, the challenge and contest topics won't be lost among the Gallery topics.
I moved some of the challenges I found from the Gallery section into this new section. But I probably missed a lot.
So if you notice any old challenges still in the Gallery section, then please let me know (you can use Report Issue link) and I'll move them.