Readied on allies summoned this turn.

[ocnarb]

What happens? They can attack like if they have haste or this don't work at all?

[Gondorian]

Hi, there.

The usual way an ally becomes exhausted is by attacking as a player action. It is also auto-exhausted as an ongoing effect on the turn it enters play until it has been readied for the first time (this is what haste effectively overrides for a summoned ally).

When does an ally become readied? Usually, this readying happens automatically at the very end of that ally's controller's turn, which is why you can use the ally properly the following turn. But some card effects can ready it before then, and so it can act like a super-haste in the sense that it even works on an ally that entered play for some other reason or an ally that become exhausted normally (e.g. through attacking).

Hope that helps!