A from-scratch, standard-library-only Go take on the classic Quartz job scheduler — no cgo, no third-party dependencies. You get Jobs (any Execute(context.Context) error, plus a JobFunc adapter and a JobDataMap for per-job state), two Trigger implementations, and a Scheduler that fires due triggers on a bounded worker pool. SimpleTrigger covers start-time-plus-interval-plus-repeat schedules; CronTrigger runs on a real cron parser supporting five- or six-field expressions with ranges, steps, lists, names and the * / ? wildcards, evaluated in any *time.Location. The scheduler adds graceful shutdown with drain, per-trigger and per-job pause/resume, configurable misfire policies, and job/trigger listeners that can veto a fire. Storage sits behind a JobStore interface with an in-memory implementation, and every fire-time decision flows through an injectable clock so schedules are fully deterministic and testable without sleeping.

$ go get github.com/malcolmston/quartz

import "github.com/malcolmston/quartz"

// A pool of 4 workers running in real time.
s := quartz.NewScheduler(quartz.Options{Concurrency: 4})

job := quartz.NewJobDetail(quartz.NewKey("daily-report"),
    quartz.JobFunc(func(ctx context.Context) error {
        fmt.Println("generating report")
        return nil
    }))

// Fire every day at 10:00:00.
trigger, _ := quartz.NewCronTriggerWithKeys(
    quartz.NewKey("report-trigger"), job.Key(), "0 0 10 * * *")

s.ScheduleJob(job, trigger)
s.Start()
defer s.Shutdown(true) // graceful drain