Do you support <accounting or invoicing program that is not Quickbooks Online>?
Not at this time.
Contact Us! We had to pick a program to get started, and we were familiar with (and use) Quickbooks Online. We're happy to look at any other accounting or invoicing service that provides integration capabilities: expanding to support additional programs shouldn't pose any significant technical challenges, other than availability of engineering time, access to the program's development environment and (of course) customer demand.
Is there a free plan?
Not at this time. We need to make sure we can keep the lights on first: once we're comfortable with the costs and usage patterns we may revisit the idea of a free plan. For now you can get started and kick the tires for a week: see if we work for you, and if not: never pay a thing!