xxl-job

Scheduled jobs scattered across servers as individual crontabs become impossible to see or control. Xxl-job handles that. It's essentially a centralized cron server with a web UI: you register your jobs, set schedules, and the platform distributes execution across your executor nodes. GPL-3.0 licensed. The admin panel shows job status, execution logs, running tasks, and lets you trigger, pause, or kill jobs manually. Supports CRON triggers, fixed-rate triggers, and API triggers. Built-in retry, timeout, failover, and sharding strategies.

Fully free. No paid tier. This is a Chinese open source project (documentation is primarily in Chinese) widely used in Chinese tech companies.

The catch: GPL-3.0 means derivative works must also be GPL. Check if that's compatible with your project. Documentation and community are primarily Chinese-language. If you don't read Chinese, you'll rely on machine translation and English blog posts. The architecture requires a separate admin server (MySQL-backed) alongside your executor nodes, which adds operational complexity.