In D&D5e a player can choose to do his standard action while moving. So a character (who can normally move 30 feet) may move 10 feet, then attack, and then move again in any direction up to his total allowed distance (20 feet). Rules like Attack Of Opportunity still hold, so when the character would move away from his attacked target, the target might have the possibility of an AOO.
I plan to include this as a house rule in my Pathfinder campaign, but I have a few concerns off the top of my head: that it might empower casters too much, and what impact it might have for clever rogues. I'm sure there are other things I haven't thought of yet, too.
What impact would this rule have on the game? Would it break the combat game somehow?