Plugins: Time/Date specific functions
Not really, and it'd be pretty difficult for PHP to truly emulate a cron service since, by nature, it requires something to execute it before it can run (in Craft's case, a browser request).

The closest thing in Craft would be its "Tasks" (completely undocumented).  Tasks are usually meant for things that might take a long time for PHP to complete and it's not critical that they happen right away.

But you can't schedule, them... if there is a task in a "pending" state in the craft_tasks table, the next request to the control panel is going to trigger it.

I suppose we could add something like a "runDate" property to tasks where you could be at least guaranteed they wouldn't run until the first control panel request was made after that given date.