The players in my game recently came across a fairly powerful magic sword as the first magic item they found. Shortly after that, they wound up in a boss fight.
The players came up with the ingenious idea of having one player attack with the sword, then hand it to the a nearby player so they could attack with it too. At the time I ruled that passing an item to another player would take an action, so they couldn't do that.
But now I'm reviewing the rules and on pp. 190 of the PHB, it says handing an item to another character is "the sort of thing you can do in tandem with your movement and action." Does this mean it's possible for the PC's to surround an enemy and just pass the sword down the line (in initiative order) so that each one can attack with the same magic sword? That seems over-powered, and a kind of ridiculous way to narrate a combat.
You might be able to do this once, if the DM allows it
The PHB has some guidance for you on this via the Use An Object option on page 193:
The section goes on to detail other more complex things that you might expend your Action on to interact with.
The relevant phrase is, 'draw a sword as part of an attack.' This is also interpreted to include things like drawing a second throwing axe if you threw the first.
Most DMs seem to be fine with, one minor object interaction per attack Action is acceptable. This might include handing the sword off to someone else, but bear in mind that the recipient has then used their object interaction to receive the weapon and would NOT be able to pass the weapon off again.