In case you have a lot of domain names with different extensions and you need all of them to open the very same site, you could have the site under one of them and redirect all the rest. There are a number of approaches to redirect one domain name to another, like the so-called domain parking. When your hosting package permits it, though, it will be better if you host each of the domains and create a URL redirect, not a domain redirect. The main difference between the two is that while a domain address is hosted, you may still have content for it, set up subdomains, email addresses, and so on., while with a parked domain you are unable to do any of those things. For instance, if you are building localized websites under several country-code domains, you'll be able to work on them, but at the same time, people will be redirected to the main website.