Technically speaking, very little has actually happened yet. Any activity between different teams or between teams and free agents who are currently under contract with an organization is not yet official. All that has been reported is the intent for such deals to be completed, and there is usually at least one deal per year that ends up falling through.
Still, it’s rare, as the Cincinnati Bengals are hoping, because the defending AFC champions used the first day of the negotiating window to try to bolster their offensive line, the weakest area on their roster. They have been reported to have agreed to terms with two new starting offensive linemen, and they likely are not done.