Is it possible to set a Wireless Access Point open for anyone to connect without having to input a pass key and at the same time have the wireless connection encrypted over the air?

What would you like to achieve by this? Why cannot users put in a one time password?

You can set multiple virtual APs with different security profiles on one radio.

What would you like to achieve by this? Why cannot users put in a one time password?

No, users can not put in a one time password. Actually i don't have to know the costumers. I just want to provide free wireless access on a secured wireless connection.

Download the hotspot package and try this http://wiki.mikrotik.com/wiki/Manual:IP/Hotspot
See also this https://www.youtube.com/watch?v=Mka4HpJQfZM

I know how to set up a hotspot. what hotspot configuratin has to do with my question?

None. You cannot encrypt data if it goes over the air over an open network. It is possible, but then the CLIENT should use encryption, like VPN, HTTPS etc....

Either YOU encrypt the air interface, or they should do it. There is no encryption without help from "someone".

And why can the people not enter a password? How difficult is that? In all cafe's I come, I see the WiFi password either written on the menu, window, or ask the waitress, or it is open, like McDonals WiFi, FON, and some airports or hotels.