GPIO Source and sink current ratings

I have looked all over and I cannot find the max current rating for sinking or sourcing current. There’s plenty of information about pin voltage, but that’s only half the necessary information… for example if I am driving an LED from a GPIO pin without an external LED driver, then I need to know how much current it can handle before I can choose an appropriate LED.

How much current can an individual GPIO pin source? How much can it sink? What is the collective current limit if multiple GPIO pins are active simultaneously?