On March, 3rd, Free plan gets two important updates:
You can invite an unlimited number of users to your Bitrix24 Account. All these users will be able to use all business tools: work with tasks, add new events to a calendar, use Bitrix24 CRM, store files on Bitrix24.Drive, etc.
You cannot assign the administrator's access permissions to the other user. To change the administrator, activate the free 30-day trial or upgrade to one of the commercial plans and follow the steps described in the article: Change the first administrator.
You can read more about tools available to Free plan users on the Bitrix24 Cloud pricing page.