Yes! you may use one Boardable User Account to gain access your multiple boards. To do so, you must use the same login email for all Boardable accounts.
Toggle between the various accounts:
Locate "switch accounts ⌄" on left-hand navigation bar below your organization's Logo (if one is uploaded).
Click "switch accounts" and a drop-down list of the all board accounts associated with your login email will appear.
You can also create another Boardable account for a separate organization by clicking CREATE NEW ORGANIZATION in the dropdown:
Tags: Users, Accounts, Multiple Boards, Multiple Accounts