Could you, say, suddenly drop a 500lb  object?

No. As the spell states:

When the spell ends, the target floats gently to the ground if it is still aloft.

Meaning that even if you end the spell before the time is up by breaking your concentration, the target would still float gently to the ground.

A round takes 6 second. Thus, you move objects Up or Down at 3.33ft/second. Or like, 2.27mph or something. Walking speed, basically.

Doubt.

What happens, if a conjurer get unconscious by wounds in the middle of the air?

Does he hang until the spell expires? Or does he fall just down?

The levitate spell is concentration. The unconscious condition included the incapacitated condition, and you automatically lose concentration if you are incapacitated. So the levitate spell would end if the conjurer became unconscious, and the spell would end. When the spell ends, they slowly hover down.

I'm guessing you can levitate a table and load it up with people and treasure up to 500 pounds and use it like a anti gravity sled?

You can. That's the best part. If you make a box for everyone, so long as it's all under 500lbs

Love this spell.

What part of gently dont you understand. Its worded so you cant use it to deal damage by dropping it on someone.

Would casting levitate on yourself save you from a fall? 

Yes and then you can end the spell and float gently down the final 20 feet

Can you levitate a weapon like a sword and attack with it from afar by levitating it side to side

Not really... But that's gm discretion because you can only move it up and down not side to side

How ever it takes an action to cast

When the spell ends it drops gently to the ground. It does not say anything about gently or the speed when moving it as an action. According to this page as it reads now as long as it is within range and Target is below you can use it to cause damage at the cost of an action so long as it is done while the spell is active.

So does the target constantly rise until it is 20ft off the ground or is that just the max that it can move within that period of time and it has to be specified? A player in my campaign was being sort of grappled by vines and he cast levitate to try to get out of it but didn't break the "grapple" so I just said he floated upright but the ones held him in the air just above the ground and would pull him down if he cast mold earth under himself since he was the target and not the vines. He made the case that the spell can move up to 500lbs worth of stuff and therefore the vines shouldn't be able to match that force so they should break, someone else said that he didn't say he moved himself up 20ft so he would just float there. Is he right or am I right in saying that he would just be held in the air a bit?

Could you combo Levitate and Catapult?

If you are the target, you can move up or down as part of your move.

If that's the case, does that mean you can cast the spell on yourself and not have it count as an action since it's regarded as movement? Or do you have to use an action first before you can use it as part of your move? 

Also, if you do use it as movement, is it still up to 20ft or can you base it off your movement speed?

Quote from Brassboy212 >>

If you are the target, you can move up or down as part of your move.

 

If that's the case, does that mean you can cast the spell on yourself and not have it count as an action since it's regarded as movement? Or do you have to use an action first before you can use it as part of your move? 

Also, if you do use it as movement, is it still up to 20ft or can you base it off your movement speed?

 

 The way I read this it seems like you can use your movement to move up or down, up to your movement speed in feet. This is assuming you don't use any movement to go sideways.