http://www.billonsite.com/
Bill On Site is a web-based invoicing system, with a unique twist: you can use Bill On Site on your mobile phone, enabling small business owners to send invoices to their customers while still on their client's site. All you need is a semi-recent phone – one with a web browser on it – and internet access on your phone.
This used to be my part-time gig, but then I was laid off and have used much of my time and severance since getting it to "release-ready" status. I just released it the first of this month, and I'd really appreciate any feedback.