NXT's account control is based on the phasing feature. It is very different than Bitcoin multisig. When submitting an NXT phased transaction the user, in addition to the transaction information, attaches a voting model and a block height stating that in order for this transaction to be executed another approval transaction(s) matching the voting model needs to be submitted before the block height is reached. Phased transactions are always included in the blockchain but are only executed if the voting model is matched. You can read more about it in the change log https://bitbucket.org/JeanLucPicard/nxt/downloads/changelog-full.txt

Account Control enforces that all transactions from a certain account has to be phased given a specified voting model and a number of blocks specified by the account control transaction. In a simplistic form, account control can be used somewhat like Bitcoin multisig, the account control transaction specifies a list of accounts which need to vote for each transaction submitted by the account under control. However voting models are much more flexible and allow many other voting options.