Harvest is everything its marketed as for time-tracking, project tracking, and Invoicing, ... and way more.
TimeTracking: My least favorite task in the world has been transformed by their easy clean interface that runs on all devices. I can start timer on my desktop, walk away, get in the car, and pick up the time on my phone. The timer registers time to Client & Project, with notes that can appear (or be edited) in your invoice. (Oh and you can track project expenses & Mileage too, with images of receipts).
Invoicing: at the end of your billing period, at click of a button you can pull all the time and expenses for a client and as many of their projects as you want billed together. You can invoice a total, or with detailed line items. The invoice editor is really clean, items can be added, removed, edited re-ordered with ease.
When you send the invoice, you can pick which of the clients' people get the email, and they get a customizable summary email with a PDF attachment, and you can include A PAYMENT LINK! for webpay. Invoices bill time at a task rate or a project rate, which you set up when you set up a client project.
Clients and Projects: list the people and projects for each client. Free version allows limited projects, so for 1st few months I bundled some projects under a client called "Misc" which worked fine. (but Harvest was so useful I soon moved to paid).
Projects are my favorite feature. Each project can have tasks with a budget of time or money (all tasks with same value, or set different costs on different tasks). As time is tracked on the timer, the time used/remaining shows graphically per task and for the whole project. This has been INVALUABLE in presenting project status to clients, as well as having instant visual on which tasks are over/under budget - so potential project over-runs can be spotted in real-time without use of spreadsheets, downloads, caluclator... and adjustments made before the project goes over budget. I LOVE THIS FEATURE!!!
Estimates: Estimates are easy to put together. I include my ToS in the notes at the bottom. The can be line items (like the invoice) or a single line summary. When you send an estimate THE CLIENT CAN ACCEPT/DECLINE with a button on the estimate. So I treat that as a signature of accepting estimate and ToS.
I also use Harvest to do all my ScheduleC business expense tracking. I have my business as a Client, with a project for each year eg: "Taxes 2016". I enter all my all my ScheduleC tax deductible expenses/mileage under that project, and add receipts as photos or PDFs. At tax time, I just run a report of project expenses and for mileage, and Voila, Schedule C done and documented!
On projects involving another consultant, I pay to add a user and have them track their time in Harvest too, so their hours are included in my project analysis and billing, with not data entry on my part.
AND I use Harvest to track all my volunteer hours, mileage and reimbursable expenses... and any other nonbillable projects that need tracking.
At present Invoicing and estimates are not available on the phone app, but that's not much of a limitation. Time & Expenses are, and that's mainly what I need on the go.
You can't save favorite time/billing reports, but reports are SO simple to run this has not been an issue for me.
That's the only mild negative I can think of