The best alternatives to Orbit for macOS are AND.CO, Hours, and Trackly. If these 3 options don't work for you, we've listed a few more alternatives below.
From proposal to payment, AND.CO takes the headache out of freelancing, so you can get back to the work that drives you. Invoicing, Time Tracking, Payments, and More For Freelancers and Independent Contractors
Trackly is a time tracking and invoicing tool for freelancers aimed at making the process from time tracking to invoicing easier by using automation to complete the invoice with the time tracked.
Ballpark gives you everything you need to run a small business in one app. Send estimates, track time, invoice clients, and keep track of cash flow, all in one place.