The D-STAR (Digital Smart Technology for Amateur Radio) protocol was developed by the Japanese Radio League and utilizes digital radio transmission for voice and data. D-STAR generally operates on VHF and UHF frequencies and allows repeaters to link with each other over the Internet. Check out the YouTube Video for more information.
Repeaters can be noted on RepeaterBook as a D-Star repeater. Links to http://www.jfindu.net/jfindu.net and dstar-users with additional information on the repeater are available on the repeater's details page.
D-STAR: Digital Smart Technology for Amateur Radio DD: Digital Data DV: Digital Voice
No pre-registration is required to utilize a DMR repeater. However, you will need to program your call sign into the radio. Consult the manual for instructions.
There is a good guide on D-StarUsers.org