I wanted a tool where you could list all your assets and debts, list all your upcoming transactions, easily specify one-off and monthly, quarterly and yearly recurring transactions, and find out when/if you'll run out of money.
I also wanted the tool to be text-based and nerdy. And free. And not to have the data leave your computer.
Spreadsheets are great. I love spreadsheets.
But if you add up all your future income and expenses, getting $1k tomorrow and paying $1k next week, and paying $1k tomorrow and getting $1k next week look the same.
If you only have $100 in the bank, one is fine, and the other is a catastrophe.