Weblate is itself a free, open-source (GPLv3+) web-based translation platform with tight Git integration, widely used by open-source projects like Debian and F-Droid — it's not proprietary, so people looking for an "alternative" here are typically after a different workflow, such as editing translations directly inside a running application instead of through a separate web-based translation UI.
Tolgee takes that different approach, letting you Alt+click strings in your live app to translate them in context.
FAQ
Is there a free, open-source alternative to Weblate?
Yes. Tolgee is open source (Apache 2.0) and free to self-host.
What's the best open-source alternative to Weblate?
Tolgee is worth considering if you want in-context, in-app translation editing rather than Weblate's separate web-based translation interface with Git-centric workflows.
What are the top open-source alternatives to Weblate?
Browse all open-source alternatives to Weblate above, or explore the full Developer Tools category for more options.