My wife and I have been using YNAB for several years now and really enjoy it. We have our ups and downs with it, but on the whole it's been a great addition to our financial lives. The main problem we have with it is just getting off the rails sometimes and not checking our balances before we purchase things (ahem, more groceries).
I've wanted a way to make certain category balances appear more prominently in places where I'm likely to passively see them. Places like on my Apple Watch, my Today Widgets, and within the app in a large, easy and quick to read way. It's not that YNAB makes it hard to see your category balances, but that I want them in my face in ways I'm not sure they'd ever add.
So that's how Allowance for YNAB was born. The You Need a Budget team announced an API a couple months ago and I jumped on it.
I also saw a potential for this to be used by people in a YNAB household who just want an answer to the question, "How much money can I spend on X right now?" People like kids in your family that have an allowance or maybe other members of the family that just aren't as interested in actively maintaining and monitoring the budget.
Hopefully it can help some of those people make better financial decisions. It's already been helpful for me.