TimeTrex is a comprehensive open source time tracking and workforce management tool, offering features like employee clock-in/out, scheduling, PTO tracking, and expense management. It is licensed under GPLv3 and suitable for businesses needing robust time and HR management.

ActivityWatch is a free and open-source automated time tracker focused on privacy and extensibility. It supports cross-platform tracking, custom plugins, browser extensions, and provides detailed reports to help users analyze their time usage.

Charm is a cross-platform time tracking software tailored for professionals, offering tools to log and manage billable work hours.

desktop-wakatime is a system tray app for Windows & Linux that provides automatic time tracking and generates usage metrics from various tools such as Figma and Postman.

Task Coach is a free, open source todo manager with built-in effort tracking, allowing users to monitor time spent on tasks. Its hierarchical task management, effort tracking, and cross-platform availability make it directly relevant for time tracking needs.

TimeSlotTracker is a Java-based time tracking tool, offering a flexible way to record and report on time allocation for different activities.