humble minion
Legend
I ran into the same issue a while ago, and the solution my group settled on was a superhero game (M&M). Every PC had to explain in their background the 'other committments' they had that would occasionally be called away by, and the nicely episodic stucture of most superhero plots (particularly the more silver age-y Saturday morning type) fit in well with our intent to run single-session self-contained adventures.
Might not be everyone's cup of tea (we use it as a backup when not everyone can make it to our primary D&D campaign), but it's an idea that works ok for us.
Might not be everyone's cup of tea (we use it as a backup when not everyone can make it to our primary D&D campaign), but it's an idea that works ok for us.