Croninfinite

Just copied the description from sandbox site: http://drupal.org/sandbox/patrickd/1182956
I think it is already a good explanation. Looking forward to the review, hoping everything is fine.
I already tested it on three different linux servers and it works perfectly, but I would be very happy if someone could test it on a windows machine.

Croninfinite allows you to run cron just like a cron job - but completely without a cron job, a site visitor or a manual cron run. It's really a kind of PHP implementation of the unix cron utility what is recommended for most sites.

How does it work?

Croninfinite depends on a script that runs "infinite".
(Before you pass judgement on this claim, please continue reading)

1. The script does not depend on a site visitors request
2. It runs with minimal system rights, a set maximum_execution_time and save mode
3. Independent from any third party service like online-cron's

The "infinite" running script doesn't run endless actually, it just times the right moment to re-execute itself just before it may gets killed by max_execution_time. I have seen this behaviour on PHP-based malware and it seems to work very solid.

How to use it?

After installation you should check out the status report page (admin/reports/status) which shows you the current status of Croninfinite. Follow the shown guidelines to Cron's settings, where it hooked into (admin/config/system/cron). Before you start, you should set the desired cron timing and the advanced settings like the max_execution_time value (if needed).

Advanced cron-timing

Croninfinite offers you a very comfortable way to time your cron runs but sometimes this is not enough and you need an advanced timing. This is what time strings are made for:
The format of time strings for advanced timing is very similar to the unix crontab utility syntax:

* * * * * <= the "time string"
┬ ┬ ┬ ┬ ┬
│ │ │ │ │
│ │ │ │ └──── Weekday (0-6) (Sunday=0) [-Weekday]
│ │ │ └────── Month (1-12) [-Month]
│ │ └──────── Day (1-31) [-Day]
│ └────────── [*/] Hour (0-23)
└──────────── [*/] Minute (0-59)

Examples:

Technical aspects and problems

The max_execution_time sets the maximum time in seconds a script is allowed to run before it is terminated. The default setting is 30 seconds. A value of 0 would enable scripts to run infinite.
Croninfinite could be enabled to run infinite by setting max_execution_time value to 0 (using ini_set()) or by expanding the maximum value (using set_time_limit())

But..

1. ..when running safe mode this setting cannot be changed while runtime.
2. ..execution could also be interrupted by the web server's timeout configuration.

The sleep() function delays the script execution for the given number of seconds. Time spend sleeping is not used to determine the time that the script has been running.
Croninfinite could be enabled to run infinite by using the sleep function between cron runs.

But..

1. ..sleeping time is ignored under Linux, but it counts as execution time on Windows
2. ..while sleeping execution could also be interrupted by the web server's timeout configuration.

The ignore_user_abort() function sets whether a client disconnect should cause a script to be aborted.
By fsockopen() a socket connection (eg. HTTP with TCP) can be opened with minimal requirements.
Croninfinite can be enabled to run infinite by restarting itself independent through HTTP using these functions. To save CPU performance it can delay the "re-spawn" by sleeping the left max_execution_time before it may get killed (read above).

But the max_execution_time cannot be determined reliable by PHP's configuration because many hosts set it to values like -1 to control it through kernel.
Croninfinite tries to assess it by executing a script that wants to run much longer than it's allowed to and time the period until it gets killed. This period should be equal to the value of max_execution_time.