The rogueish archetype Thief gets the feature Fast Hands:
Starting at 3rd level, you can use the bonus action granted by your Cunning Action to make a Dexterity (Sleight of Hand) check, use your thieves’ tools to disarm a trap or open a lock, or take the Use an Object action.
It has been established that the fiery blade from Flame Blade is not a weapon. Assuming the Thief has some means of casting Flame Blade, could the Thief use his Fast Hands feature to use the Use an Object action (as a bonus action) to attack with the fiery blade?
Since the fiery blade isn't a weapon, but it is a thing, I figure it should be close to an object (looking at the answers to this question certainly imply it is). The spell also has very similar wording in how the fiery blade is used as many objects. Compare the description of the fiery blade:
You can use your action to make a melee spell attack with the fiery blade...
to the description of Acid:
As an action, you can splash the contents of this vial... make a ranged attack...
or Hunting Trap:
When you use your action to set it...
Does the fiery blade count as an object, and therefore can it be used with Fast Hands, or is it something distinct?