It's a bit hard to find, looks like they've given up trying to compete for non-business users, but the client has a registration form open to everyone.

I think they'll keep supporting this because inviting those 'guest' accounts into rooms of business users is a big feature. We regularly collaborate with people via Wire (customers or freelancers, who can just use their personal Wire accounts) because it's the easiest way to collaborate without forfeiting encryption or features.