Kimai vs ActivityWatch vs TimeTagger — Best Open Source Time Tracking Tools Compared

Time tracking is one of those things almost everyone should do and almost nobody enjoys doing. The proprietary apps that dominate the space lock your timesheets into a subscription and a cloud you don’t control. Open-source trackers flip that: your data stays on your own machine or server, and you can keep the tools as long as you like. The tricky part is that they solve genuinely different problems — Kimai is built for teams and billing, ActivityWatch tracks automatically with zero effort, and TimeTagger is a lean pick for individuals and freelancers. Let’s compare them honestly so you can choose the right one.

1. Kimai — The All-Rounder for Teams and Businesses

Kimai is the workhorse of the group: an open-source time tracker aimed squarely at project-driven teams and companies. It’s written in PHP (Symfony) and trusted by more than 7,000 businesses, and it turns simple timesheets into the data you need for invoicing and reporting. You can run it on your own server with Docker or pay for the managed cloud — same features either way.

• Built for teams — multi-user setup with customers, projects and activities lets everyone log against the same structure.
• Real invoicing — configurable invoice templates, entry grouping, custom invoice numbers and PDF/DOCX export.
• Expense tracking — capture costs alongside time so billing reflects the full picture.
• Reports and analysis — break down recorded time by user, customer, project, activity, tag or time period.
• Enterprise auth — login via LDAP and SAML (Google Workspace, Azure AD, Authentik) plus optional TOTP two-factor authentication.
• JSON API and plugins — an extensive read/write API for custom tooling, plus a plugin marketplace to extend it.

2. ActivityWatch — The Automatic Tracker

ActivityWatch is a different animal: instead of logging your time by hand, it tracks your apps and websites automatically in the background. It’s a privacy-first, cross-platform alternative to RescueTime, ManicTime and WakaTime, running natively on Windows, macOS, Linux and Android — and, crucially, your data stays on your device and is never uploaded anywhere.

• Zero manual logging — automatically records the active application and window title out of the box.
• Local and privacy-first — data is stored on your device and never leaves it unless you sync it yourself.
• Browser and editor plugins — Chrome/Firefox extensions track your active tab; editor watchers track how you spend your coding time.
• Categories — automatically groups your usage so you can see screen time broken down by type.
• Cross-platform — Windows, macOS, Linux and Android, with the UI served locally in your browser.
• Community-built — maintained entirely by volunteers, with an open development process.

3. TimeTagger — The Lean Pick for Individuals and Freelancers

TimeTagger does one thing and does it well: quick, tag-based time tracking for individuals and freelancers. Built around an interactive timeline, it’s designed to give you instant insight into where your day went, and it replaces heavy project hierarchies with simple, flexible tags. It even runs offline and syncs your data automatically across devices.

• Interactive timeline — drag and tap your way through time for fast, visual tracking and immediate insight.
• Tags, not projects — a lean, versatile model that avoids rigid project structures for solo users.
• Powerful reporting — generate PDF reports to bill clients and export to CSV for spreadsheets.
• Offline-first sync — keep tracking with no connection, then auto-sync when you’re back online.
• Dev-friendly — a web API and an official CLI tool let you track time from the terminal.
• Open source — GPL-3.0, self-hostable, with a transparent development process.

Head-to-Head

How You Track Time

Kimai and TimeTagger are manual: you start and stop a timer or log an entry. ActivityWatch is the only one that tracks automatically — it watches your apps and windows for you. If you’ll never remember to click start, that alone decides it.

Who It’s For

Kimai is the team platform — multi-user, with customers, projects, activities and permissions for organisations. TimeTagger is aimed at individuals and freelancers. ActivityWatch is for individuals who want to understand their own screen time and productivity rather than bill a client.

Billing and Invoicing

Kimai is the clear winner here with full invoicing, expense tracking and PDF/DOCX templates — it turns timesheets into bills. TimeTagger covers freelancers with PDF reports and CSV export for client billing. ActivityWatch has no billing features at all; it’s an analytics tool, not a billing one.

Deployment and Platforms

ActivityWatch is the easiest to get going — install a native app and it runs. Kimai needs a server, but offers one-command Docker self-hosting or a managed cloud. TimeTagger is a web app you can self-host or use as a service, and it works offline and on any screen size.

Data and Privacy

All three keep your data under your control. ActivityWatch stores it locally by default and never uploads it. Kimai self-hosted keeps everything in-house (its cloud is GDPR-compliant, EU-hosted). TimeTagger can run entirely on your own servers with offline capability.

Which One Should You Pick?

Choose Kimai if you run a team or business and need multi-user tracking, invoicing, expenses and reports — it’s the all-rounder that turns raw timesheets into bills and client-ready PDFs.

Choose ActivityWatch if you want automatic tracking with no manual effort — the best way to see where your screen time actually goes, without logging a thing.

Choose TimeTagger if you’re an individual or freelancer who wants a fast, tag-based tracker with clean reporting and a smooth, offline-friendly experience.

The Bottom Line

These three aren’t really competing for the same job. Kimai is the professional team and billing platform, ActivityWatch is the set-and-forget personal analyst, and TimeTagger is the freelancer’s lean favourite. What they share is being genuinely open source with your data fully under your control — more than any proprietary competitor can promise. Pick the one that matches how you work, and you can’t go far wrong.

Get Started

Kimai and TimeTagger are free to self-host, with hosted options if you’d rather skip the server; ActivityWatch is free to install on any desktop. None of the three are in the directory yet, but you’ll find plenty of compatible productivity tools in our Task Management directory, or explore the full free and open source collection we’ve curated.

Know a great open source time tracking tool we haven’t covered? Submit a tool and help us grow the directory.