When brands come to Farcaster, they will need a tool that lets multiple community managers login with their email (probably) and manage the account. This can easily be done with Signers. 

Who's building the corporate farcaster account management tool? Who's integrating this functionality to their existing tool?

I'm absolutely interested in that! It would also be cool if it worked with one contract, which was managing the members. So for example an @aragon App based guild, is able to manage the account, and has 10 signers (as example).

possible to do this with offchain user accounts in @herocast soon.
working towards an onchain solution with this @hatsprotocol 

Searchcaster