There is a cryptocurrency similar to Bitcoin called NextCoin and a new client available for NextCoin is built in Delphi XE5 Firemonkey. The client is called NXT Solaris and full source code is available for the client with a GNU license. Currently the source code is for Windows 32bit and Windows 64bit but Mac OSX support is also
planned now available (Android and IOS support are not mentioned). The NXT Solaris client uses the LkJSON library which doesn’t look like it is cross platform yet. NextCoin according to this page is a descendant of Bitcoin but is brand new software not not a fork of the original source code. It is a proof of stake currency where coins are earned by charging transaction fees. Mining in NextCoin doesn’t cause monetary inflation. NextCoin claims to have many improved features over Bitcoin including a resolution for the big environmental issue.
Update: The Mac OSX version source code is also now available.