Time tracking only works if the app is not annoying enough that you stop using it. The four below survive that test.
1. Toggl Track — the gold standard
Free tier covers unlimited tracking, projects, and clients. The one-click start/stop button is the best in the category. Reports are exportable as CSV for invoicing.
2. Clockify — Toggl but with more free features
If you need team time tracking, Clockify's free tier is unmatched. Unlimited users, unlimited projects, full reporting.
3. RescueTime — automatic, no buttons
RescueTime tracks automatically based on the apps and websites you use. No buttons to press. The "Lite" tier is free and shows you how your day actually broke down — often a sobering experience.
4. ATracker (mobile only)
Best mobile time tracker. Single-tap to switch tasks. Free version covers most use cases.
How to actually use them
The mistake is over-categorising. Start with 4 to 6 categories: "client work," "admin," "learning," "meetings," "deep work." Run for two weeks. The patterns will surprise you.
One specific habit that compounds: end every day by checking your week-to-date totals. Five minutes of reflection prevents fifteen hours of drift.