The main features I found missing in other budgeting apps that prompted me to make my own were:
- native multicurrency support (I travel a lot and am a digital nomad by lifestyle, so this was quite important to me)
- curtains pulled on the "magic" that some budgeting apps try to add to my transactions
- the ability to split/group transactions so I can see how much I actually spent when I pick up a large bill and friends pay me back
- separate tracking of recurring expenses
- seeing historical spending trends and having information help drive my budget for the next month
I've implemented all of this and more. If you're interested, check it out at https://lunchmoney.app. I'd love to hear what you think.
In terms of what's missing that's not currently on the roadmap:
- rollover budgets
- a savings and/or goals feature
- debt repayment feature
As made evident by this thread, everyone has their own preferred way to budget, and of course there is no one-size-fits-all solution. Looking forward to seeing what you build, if you end up going down that path. Cheers!