Using Web Part or User Control in another web site

Dear All,
 
I am not sure if I am doing it correctly. Basically, I need to enable some one from another web site to display something that is hosted in my web server.
 
The content are actually in the form of User Control. But unfortunately it is almost impossible for the other web site to re-use that User Control without copying 90% of the code from my site. I am trying to use Web Part, but at the end, facing the same problem.
 
So, my questions are:
1. Am I using the User Control / Web Part correctly? Or is it possible for someone from other web site to use my User Control wihtout copying the code behind page?
2. If not possible, do I need to use something like <iframe> or even the <frame> element to do this?
3. Any other alternative?
 
Thanks in advance
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