Originally Posted by MeGustaDragons
It used to be an older summoner spell (like heal, exhaust, ghost...) , but has since been removed from the game. It could be used to rally minions to a certain area.
Don't know why it still did that though. Must be a bug.
Correction: Created a banner with around 200 hp (depending on champion Lvl) which increased the AD (I think AP as well if you got the mastery for it) of all nearby allied units. Replaced by Promote.
Edit: I mean the new Promote, usable in Summoner's Rift... oh and I just realised it was Surge that 'replaced' Rally (was said to be an AoE boost, like On the Hunt in the announcement), and Promote replaced Fortify (somehow...)