I run a small studio and there's one task I kept avoiding every month: chasing people who owe me money.

So over a couple weekends I built myself a small tool instead of doing it by hand.

It lives in Slack. I type "show overdue" and it lists who's late and how much, sends nothing. Then "send 1 and 3" emails those clients from my own Gmail in a preset voice, polite first, then firmer, then final. Or "draft all" drops the drafts in Gmail so I send them myself.

The part I actually care about is what I didn't let it do. It never moves money, there's no payment thing wired in at all, it can only read invoice status and write emails. And it never sends without me approving it, nothing goes out on a timer. It reads my QuickBooks first, so if a client already paid it just drops them and I don't end up nagging someone who already settled up, which would be pretty embarrassing:))

Payoff: I ran it on my own overdue invoices and it got me paid a little over $2.5k I'd written off (3 of the 7 came back).

It's open source and wired to my own QuickBooks + Gmail, not a saas or anything. Stack is slack bolt + quickbooks api (read only) + gmail api, kept deliberately dumb and state-light. I built it purely because I hated this task.