My brother told me about this last week and I've been pretty impressed with it so far. For years, I've used the Mac app Billings to do my invoicing. But lately, I've been finding it necessary to access my invoicing and estimates on the go which Billings has been lacking except through a paid tier on their website. I wasn't in love with Billings to jump aboard and start paying there so I never did.
Intuit's Quickbooks was another alternative I considered but it too was a paid service which I just didn't find necessary considering that I didn't need all the extra stuff -- just the ability to create, edit, and view invoices/estimates on the go. I gave up. I figured all apps and services were moving to paid tiers which I thought just sucked.
But then I found out about Hiveage (which used to be called Curdbee). It is a free service that does everything I need it to do with paid EXTRAS if I need it. It's the kind of service I've been looking for and so far has been quite amazing and easy to use. Reports are beautifully and automatically generated and overall, Hiveage takes the work out of invoicing and billing so that I can spend as little time as possible inside Hiveage. It works.