There's a number of backend software providers. All of them have got experience in running registries but they differ in prices, services, company structure, interfaces, coding etc. Some backend providers are currently running registries while others have seen a potential spin off and created seperate companies focusing on delivering backend solutions and added services.
Choosing a backend service provider depends on how applicants expect to use their .brand TLD, needed services, wishes for interface, security issues etc. I've listed some of the providers below - in alphabetic order.
Afilias is an Irish Limited company with international headquarters in Dublin, Ireland. Ownership consist of a number of registars. Afilias is most known for launching and running the .info registry but they are also software registry providers for a number of other gTLD's as well as some ccTLD's
AusRegistry is a wholly owned subsidiary of AusRegistry Pty Ltd, the current Registry Operator of the .au ccTLD. AusRegistry also provide Registry Software Services for the .ae Domain Name.
Central Registry Solutions is a partnership between Network Solutions, LLC and CentralNic Ltd. CentralNic is providing registry services for us.com, uk.com, .la amongst others.
CORE is a not-for-profit membership association of Internet domain name registrars and registries. CORE has supported the launch of .aero, .museum and .cat as backend operator.
Minds + Machines is focusing solely on new gTLD's. Their backend software "espresso" is based on the open source backend provider CoCCA's registry platform. CoCCA serves as registry software provider for approximately 20 ccTLD's - .af, .cx, .cm, .pe to mention a few. Major shareholder in Mind+Machines is the publicly-traded company Top Level Domain Holding, Ltd. - listed on London Stock Exchange
Neustar is providing registry solutions for .biz, .cn, .us amongst others. Neustar is operating .biz and .us and they launched .biz back in 2001 under the name Neulevel which was originally a joint venture between Neustar and Melbourne IT.
RegistryAsp is a division within Qinetics Solution Berhad. RegistryAsp is delivering registry solutions for .sg, .hk and .cd.
Verisign is of course operating .com and .net and they are providing registry backend solutions for a number of other TLD's.
History, focus, track record, services and prices differs amongst these providers. Change of backend provider is possible while running an own BRAND TLD but it's of course a costly affair so choose your backend software provider carefully.