Looking for a decent time-tracking application for Mac

I am a freelance graphic designer and need to track the time spent on projects so I can bill my clients accordingly. There are a ton of services and applications out there but somehow none of them really fits.

Here's what I am looking for:

• A stable desktop app. I don't want to do my time tracking in the browser.
• Stop recording when screensaver or sleep mode starts.
• A product I can buy, not a subscription service. I feel more comfortable and in control if I pay $100 upfront than pay $10 a month
• An easy-to-use UI that tracks time by client, project and task.
• Billing support is a bonus, but not necessary.

Here is what I don't need, so if the solution contains it, at least is shouldn't interfere with a simple workflow and efficiency:

• Not necessary: Smartphone app, team collaboration, cloud.

All I want is a pay-once, stand-alone, well-supported and nicely designed time-tracking app. Do products exist in this space for OSX?

I am listing the apps I have looked at so far. I must emphasize that none of them really solves the problem stated above perfectly.

Here's what I have looked at so far based on my google doc list

• On the Job looks great, but the developer seems to have abandoned it. At least he does not really fix bugs and is very slow to respond to his user base.
• Timings light-weight but the UI to create clients, projects and tasks can be confusing. I am testing it right now. A friend uses it and says it crashes sometimes though it has not happended to me yet.
• Harvest looks good, it does have a desktop client itself and an API that is used by lots of apps. But it is subscription-only which is a no-go for me and costs at least $12 per month.
• The same goes for Toggl: looks good, but is subscription-based and costs $5 per month
• iBiz and timeEdition have been discontinued
• Klok is an Adobe Air app. The UI feels weird. Small typography, limited support for keyboard shortcuts and complex interface.
• OfficeTime feels like the best match so far but the UI is very cluttered (see this screenshot of the Generate Bill dialog as an example). It feels a bit like a Windows app that has been ported to Mac but I am not sure if that's true.
• Timecop is a very minimal approach. There is no way to test it without paying the $6.99 price. Has not been updated for 9 months, twitter account has been inactive for 5 months.
• Tictoc seems very similar to Timecop. No way to test without buying either.

I haven't found the one I like and I created it myself, Qbserve.

It fits most of your requirements:

• native stand-alone macOS app
• detects idle time
• comes for a flat fee ($40)
• supports projects and tracks time for them automatically (based on opened documents and web pages) but it's also possible to assign time manually
• generates invoices from the tracked time

It also automatically recognizes productivity for sites, apps, and chats (you can assign Skype chats and Slack teams to different categories).

Plus all the tracked information is stored locally on your machine in an SQLite database.

Been using Tyme for quite a while and pretty happy about it. Available for OSX ($9.99) and iOS($3.99).

I'd like to recommend my own app Timing, an automated time tracker (see the screenshot below). It automatically tracks which documents you edit and which websites you visit, so that you can later review what exactly you have done. You can also manually add offline activities so that they don't get lost.

Let's see how it fares with regard to your requirements:

• A stable desktop app: Timing runs on your Mac and stores all your data locally. No internet connection required!
• A product I can buy, not a subscription service: It's $24.99 one-time (currently reduced to $19.99).
• An easy-to-use UI that tracks time by client, project and task: Timing records each activity individually, and you can then drag it onto a project. For clients, you could create a parent "project" that all subprojects are a part of.
• Billing support is a bonus, but not necessary: Sorry, Timing does not support billing. But you can export your tracking data as CSV or JSON to be used by your billing app of choice.
• Regularly updated: I'm updating the app all the time, as the release notes show.

I've started looking at TimeLime. It's a paid app available on the Mac App Store. I've heard a lot of good things about it from other users I've chatted with.