NS Name Split takes the core Joomla registration 'Name' field and converts it to 'First Name' and 'Last Name'.
When a user registers on your site it will take the first and last name entries, insert them into a database table the extension creates on install. It will then merge the name together (i.e. first.last) and insert it into the core name field/table.
This method avoids core hacks so your site can be updated when new Joomla versions are released. Keeping the core name field intact ensures that other extensions can still use the name field to function normally.
v2.2 - 24 Aug 2013
Added Joomla 3.x compatibility
Cleaned up UI
v1.2 - 25 Jul 2013
Initial release for Joomla 2.5