Basically every major budgeting app I've looked at doesn't allow rolling buckets of money. For example, my wife and I budget $X per month for travel, but we only travel once or twice a year. What I'd really like to be able to do is allocate some amount every month to certain activities and have my budget keep track of how much I've saved for that purpose.

On the other side, sometimes it's hard for us to reconcile our food budget between months. If we have a big grocery trip on the last day of the month, we kind of expect to spend less the next month but won't always remember that when we go reconcile our budget.