I've had a Simple account for a few years, I use it for my non-bill, smaller expenses (dinners, lunches, groceries; I don't use it for things like new tires on my car). A nice thing with it is "goals". I set up a goal for June Dinners. I set aside $200 for it. But I have it fill out the goal over the course of the month. So on the 1st I have $7 (keep the math simple, I'm rounding) on Day 1. On Day 2 I have $14, etc. Now it's Saturday, 2 June, I have $14 I can spend on dinner out with friends. That means water, inexpensive entree, and no alcohol or dessert. If I saved it up for another week I'd have about $63 available. I like this method of "accumulating" money across the month (or months, for some expenses).

Prior to that there was an app called "Level", that did the same sort of thing across all your accounts. However it consistently failed to connect to my primary bank so it wasn't that useful.