Google Contacts, the address book built into Gmail, lets you keep track of all your contacts, see when you last interacted with them, and more.
Record signature request links on the right client cases.
Your signers get the agreement to sign, and you can see the request link and sent status on the case.
Send the approved agreement and record which version went to signers.
Your agreement goes to the right signers in the order you choose, and the case gives its owner a link to the request.