How to insert more keywords to one field

Hello,

could you please recommend me any module for adding more words to"keywords" to one field during creating new content?
I like something like Chosen provides, e.c. when you have Text List and you apply Chosen module, you can add more options from that list which looks like this: http://kejmil.melnicek.cz/offer.png

BUT ! I DO NOT want to be fixed on list of available options. I want people to write whatever word they want and how many they want and just by ENTER to add them to this one field. I also do not want to use comma necesary for separate each keyword.

Please, is ther any module which can allows that?

Thank you