update below refutes a assertion I made.
Tao Naming Service
Three major levels comprise the TNS. Sig Chains, Namespaces, and Global Names. These different levels offer different characteristics for users, but do not provide an entirely clear value proposition, particularly Namespaces. Signature chains are a core aspect of Nexus, while Namespaces and Global Names are somewhat peripheral.
Sigchain usernames are unique identifiers, no two usernames in the entire network match. However a variety of symbols are acceptable, including spaces! You can create sig chains which consist entirely of spaces. I won't go into exactly how sigchains work, but before any user interacts with the Nexus blockchain they must create a sigchain.
Any signature chain can buy, own and transfer Namespaces and Global names from the network. Owning a Namespace allows an user to create accounts, tokens, and assets based on the Namespace rather than the signature chain. Instead of the typical Username:account addressing, Namespaces provide alternatives to your username and area addressed Namespace::account. Nexus restricts Namespaces and Global Names to lowercase letters numbers and periods. Global Names act as unique global identifiers, avoiding the need to identify through username or namespace altogether. Employing the same character restriction, Global Names aim to fill needs where a single identifiable name is desired, such as token tickers.
Personally I hold some concern around name squatting for signature chains. These are the only FREE unique identifiers I know of in the network, and also are quite powerful. Besides the slight anonymity, which isn't helpful since you can find the owner of the namespace through the /Names/get/namespace command, all they offer is an alternative name in a more restricted naming environment. Other blockchains trying to get rid of long addresses like 0x49F761932707ABE68a669E8d235a25f589827e16 might find significant value in a naming service, but in Nexus simply creating a new sigchain provides an easy unique name, and it's free.
Nexus reduces the incentive to poach names by making usernames easily unique through a space or dot at the end of the name, but this leads into another usability issue. What happens when people want the same name and just add spaces to the end? The names end up looking all the same but are different. Users will need to decide on a way to communicate spaces effectively and remain vigilant in making sure they type the right name.
***Update after a discussion with a few folks in the Nexus slack I received a heightened understand on why the namespace at least offers some privacy and separate function compared to sig chains. While the Genesis ID of the namespace owner is easily found, one cannot derive their username from just the genesis ID, so creating a namespace can preserve your username. Also accounts created in namespaces can "point" to any address on the blockchain. So for example if I ran a company with namespace Tesla and had a CEO bob I could create Tesla :: CEO account, and point the address at an account that Bob owns. Any payments to Tesla :: CEO account would go directly to Bobs account. If I fired Bob and added someone else I would just point the account to a new address. This isn't the most groundbreaking naming use case but for corporate instances Namespaces seem somewhat attractive.