I'm implementing a wait() function, which I want to be multiplatform, and hopefully not use sleep().

Are there any functions on win and linux that allows you to just relinquish cpu time immediately?

I realize that sleep() does this, but I want to know what the alternatives are?

I'm guessing there are none, but I'm asking anyways.

I do not like the sleep function because it causes a fixed delay. I would loop a little bit and use the clock function. It is under the ctime namespace or I believe time.h

Neither system is a real-time operating system. You can yield your time, but there are no guarantees about when the OS will reschedule you.

In fast-paced games usually the best bet is to wait for the screen buffer to flip. The major rendering APIs have blocking calls for that.