Hi, we do provide the serverside-coding part , the client-coding part . Here you have the choice :
1- JNLP(Java) , because JNLP automatically detect the version of the JVM and install the right one if needed and download all the ressources that belong to the application and Java is multi-platform(linux,windows,mac,etc)
2- C++, but we have to recompile with each platform , that is a little more expensive; to give an idea for the windows platform we can use C++ with Flash design.
We , you and we, can coomunicate and discuss more about that project ,your preferences and your needs, then we start immediately.
Regards.