<Foo>
{ (thingy) => <Bar something={thingy}/>}
</Foo>
.As Ryan Florence or even his holiness Dan did during this ReactConf:

It makes no sense. The original "render prop" is a prop, called "render" and used to bypass the normal component’s way of rendering by passing to it a function that it will use instead during rendering. Even React's docs still adhere to this conventional meaning by showing this prototypical example of a render prop:

The other one used to be called the "function as child" pattern. But now all the cool kids call it the render prop :-(
[Another rant]
(as an aside: you miserable LJ and your crappy editor that constantly is breaking my bit of JSX! why aren't you allowing raw code in pre tags any longer, you bastard?)