cronbot is a wrapper script for cron jobs. Rather than running your job/script directly, you run it through cronbot, and it will allow a little more control to help keep things from getting out of hand. The default behavior is to only allow one instance of your job to run. This can be changed with the --duplicate option. You can also pass in a maximum time of execution for a job or add a random amount time to delay the start of your job. By default, jobs are run with a default "nice" value, which is usually 10.
TimeMachine Scheduler is a Java scheduler which can scale and run a high volume of jobs with many different types of schedules, such as repeating on a fixed interval or based on cron expressions. The scheduler can control the job executions with thread pools, and it can persist job data into different storage receptacles. Users may use the built-in schedule server with an easy-to-use configuration file, or developers may use it as a library to extend the scheduler and write custom jobs, schedules, or user services.
Bidwell (named for Shelford Bidwell, the inventor of the first true fax machine way back in the late 1800s) is a set of Perl scripts that are designed to run as a cron job on a Unix-like system to download emails from a POP3 account and send their contents to a CUPS or lpr printer.
Schedule::Cron is a Perl module that provides a simple but complete cron-like scheduler. It can be used for periodically executing Perl subroutines. The philosophy behind Schedule::Cron is to call subroutines periodically from within one single Perl program instead of letting cron trigger several (possibly different) Perl scripts. Everything under one roof. Furthermore, Schedule::Cron provides a mechanism to create crontab entries dynamically, which isn't that easy with cron. It knows about all extensions (at least all extensions the author is aware of, i.e those of "Vixie" cron) for crontab entries like ranges including 'steps', specification of month and days of the week by name, or coexistence of lists and ranges in the same field. It even supports a bit more (like lists and ranges with symbolic names). It has existed since 1999 on CPAN and is successfully used in many projects.
runcronjobs processes the execution of centralized cron jobs for a pool of servers. The cron jobs are any executable files. runcronjobs runs cron jobs located in a given directory if the current host is specified as a target host for the jobs in question. It allows you to centralize all the cron jobs of a set of servers in a common shared directory.