I don’t know if it already be proposed but I tried amazing Marvin and even if it doesn’t build around GTD I think some features worth it :
weekly review tasks : people add custom task and it appears during weekly review. For example _clear mind _review project _thinking about…
back burner : it serves to ‘store’ tasks to hide it from list but keep it for later like monthly review. Kind of someday list.
What do you think of these features ?