RSS Feed in to my site?

I have multiple sites and would like to be able to write one blog and have it feed the others as if they were being written on that website.

For this example I will say the main website is called mainsite.com and the other website is called anothersite.com

I would like it so when viewers go to anothersite.com they are reading the blog as if it was written from anothersite.com and they would have no clue that it was actually written on mainsite.com.

How would I do this?

I don’t mind using plugins if anybody knows of any?

Thank you for your help.