Threesomes aren't the be all and end all of more-than-two sex, foursomes and moresomes are also common in some fetish clubs and sex-positive social circles, and sex involving four or more people is often referred to as 'group sex'. There's more than one form of group sex - there's the gangbang, for example, where a group of people are all focused on one individual, and there's the orgy, which is more of a free-for-all. People of all and any sexualities and gender identities can enjoy group sex in the right context, and it's a great way to live out some of your deeper and darker fantasies.
Safer sex is even more important in group situations than it is in most others, as there's a far higher chance of picking up something you didn't want when you have more partners at once. You should also have consent negotiations before, during and after--it's vital to make sure that everyone is happy, comfortable and on the same page.