Frostmarrow
First Post
One way of doing it would be to disconnect effect from chance of success. Say you roll a d20 under your score to succeed and then follow up with a d6+bonus for effect. Then it would be equally simple to set up skill challenges for a single character as for an entire group. If you need to swim across a pond with DC 10 you'd first roll under Str 17 and when you succeed you roll 1d6+3 to make progress. Once you reach 10 you've crossed the pond. If your entire group need to cross maybe the DC is 30 but all characters get to contribute to that the pool of progress. Moreover each round the challenge is unresolved something bad happens (time passes, fatigue, hp loss). If you have a Swim feat maybe your effect amounts to 1d8+bonus.