That is called NAT64 and there are a couple of other techniques (eg IVI) out there which can solve that scenario. At the moment though most applications require native IPv4, and thus just doing NAT for IPv4 and native IPv6 is the best and easiest way to go.

An open source solution can be found here: http://www.litech.org/tayga/ For theory of both "Stateful NAT64" ans "Stateless NAT64" see: RFC6144 - Overview RFC6145 - How IPv4 <-> IPv6 translation works RFC6052 - How IPv6 addresses are translated to IPv4 addresses and vice versa RFC6147 - DNS64 which is needed to synthesize AAAA-RRs for IPv4 only destinations. In addition "Stateful NAT64" is described in RFC6146. You would use Stateful NAT64 if you only want to access IPv4 Internet destinations. Your Internet access must also provide native IPv4 with at least 1 public IPv4 address which is needed to represent any IPv6 source address from within your LAN. If you want IPv6-only servers within your LAN to be accessed from the IPv4 Internet, you need Stateless NAT64 instead. But then your Internet access must also provide native IPv4 with at least as many public IPv4 addresses as you want to operate IPv6-only servers within your LAN, because each of those servers needs an IPv4 address that represents it within the IPv4 Internet. The above mentioned Tayga solution only implements a Stateless NAT64, but if you combine this with a standard PAT device vor IPv4 (e. g. your standard IPv4 NATting Internet access router) and configure the Tayga device to translate IPv6 addresses 1:1 to a pool of private IPv4 addresses, the combination of both devices operate like a Stateful NAT64, see the readme file for Tayga. The Tayga implementation deviates from the standard defined by RFC6052 in that it also allows the configuration of a mapping table to map IPv6 source addesses to any IPv4 addresses instead of using "IPv4 translatable" IPv6 source addresses as required by RFC6052. IVI as described by RFC6219 is another solution for Stateless Translation and obeys to the same principles, but it was invented before Stateless translation was standardized by the above mentioned RFCs. It deviates from RFC6052 in the way IPv6 addresses get translated to IPv4 and vice versa.