This is my version of Gazelle and Xero rolled into one app, which I use to keep track of the piano technician side of my business. I don't want customers to sign up appointments by themselves online (yet), and I don't have the throughput to justify the expense of either application. So I have built my own simple system.
Others are welcome to try it, and I welcome beta test input, but in order to use invoicing and their sending via email, I'll need to set you up: You'll need a logo for your business and you'll need to verify that it's OK for this system to send invoices from your email address (Otherwise no spam filter is going to let your invoices through.)
I have developed this for my work in New Zealand, but if there's interest elsewhere I'm happy to modify the invoicing to suit the needs of other locations. You'll have to tell me what those are, however.
You can login as guest/guest to see how it works (the DB is populated with a few fictional customers).
Otherwise, contact me for a login.