This could be something built into the hypothetical framework I mentioned. As in, the default quoting template for your industry has x% upfront payment terms, and you deselect that option after a strong warning. All my quotes asked for 20% up front but then I almost never bothered invoicing it until I was finished, so I would need something that auto-invoiced the 20% when the client clicked "Accept Quote"... ;`(

Then the time-tracking component would strongly warn against commencing work until the invoice was paid, etc.

So, basically, a very opinionated business framework web app.