Invoicemaker.org is a free online invoicing tool built with Laravel. The beautiful invoices are created with wkhtmltopdf, making the design very flexible. Registered users can send PDF invoice as an attachment directly to their client. Other services watermark the PDF, or don't put the PDF directly in the email, but a link to it at their service. The service even lets users monitor if and when their clients opened the mail via a 1×1px PHP produced white image included in the mail. After billing a client once, the system saves the client address data and ajax autocompletes it at future uses for the users convinience.

I developed this as project to learn how to make nice PDFs with Laravel and was my first use of jQuery beyond using plugins. When using tables, PDF libraries become pretty tricky. What sets invoicmaker.org apart from other free invoicing sites is that they are often made by paid services as a promo. They brand the PDFs so that users upgrade. Other simply don't produce good looking invoices someone sane might want to send their client. The best opportunity to monetize a free invoicing site is to keep it basic and be an affiliate site. Not to offer a shitty product so that users pay for the service, but to serve freelancers in their starting phase who later need a more advanced product. When self employed people start out, often maybe as secondary income, they would most likely use a free service to quickly produce good looking invoices. When they progress and eventually succeed they will have seen the advertising for more features on invoicemaker.org. It will probably make a good percentage consider clicking on a "more features" type of referral link. Invoicing/Bookkeeping SaaS have long user retention durations because they are both convenient to use and inconvenient to change. This keeps lead compensation high. For affiliate site opportunities this is one of the best i have come across. It not only “captures” potentially interested parties at the right time in their career, it also seems logical that while using free services for invoicing business owners would want to keep invoice design consistent, making return users very likely. One of the biggest invoicing/bookkeeping SaaS sites offers an affiliate program paying $100 per lead, but it only accepts affiliates that can deliver a certain undisclosed minimum volume and will have to be manually approved.

I want to sell invoicemaker.org now, because I'm not interested in promoting it to the point where it becomes a passive income stream. It was a learning opportunity for me and I will use what I have learned on a different project. An interested buyer would have to get a consistent user base before securing good affiliate partners, but after that can cash in one a very lucrative niche. To run this you will need a VPS and a (free) mailgun.com account would be best for a good invoice email delivery success rate. A cheap $10/mo. linode is more than sufficient which will keep running cost until monetization very low. The negatives: it comes without users & the JavaScript was my first try and is ugly butchered together, but works very well.

Price: Relativly flexible on the price. Make an offer.