I've been putting together a no-nonsense free invoice generator, for people (like myself) that only occasionally send invoices. It's more-or-less a WYSIWYG editor, and the state is stored in the URL, so you don't have to worry about keeping track of where you stored your copy - if you've sent someone an email with the link, you've got a copy. This project was born out of the frustration of trying to generate an invoice on my phone on the go, I found all the existing solutions to be quite awful (forced signups to paid subscriptions, clunky interface etc).
Would love to hear any feedback the HN crowd has. I'm aware of a couple of alignment issues, will fix them up tonight. Also, yes, there will be a "generate PDF" button, for now if you want a pdf I'd suggest using the Print dialog to "Save as PDF".