Do you have any employees? I use almost all free products, but it's just me. I use Google Keep to keep track of all the minutia. I use several labels, the ones I use the most are Call List, Message Left, Scheduled and Parts Ordered. I also have a Limbo label where notes usually go to die. I also have To-do label but rarely use it, those notes usually end up on my call list. You could have an Invoice label but I use my calendar to remind me to invoice. I use Google Calendar for scheduling. Even though Keep and Calendar are both Google products, they don't integrate well. I use a free app called Business Calendar as a go-between. When I'm ready to schedule, I'll send the note to Business Calendar which updates my Google calendar almost instantly. I use desktop Quickbooks to keep track of invoicing, it is not free. There is a free option called Waveapps which I haven't used. It is completely free, the only cost is from an optional added payroll service and the 2.9% + .30 transaction fee if you use them to accept credit card payments. The only reason I haven't used them is my wife uses Quickbooks at her work and I would lose her help with bookkeeping and taxes if I switched.