This is written in C# .Net and makes use of WPF. This is not supported on Mac or Linux systems last time I checked. Java Stand Alone and Java Applets (what is this the 2000s, does anyone still use applets?) are a completely different programming language and would require rewriting the entire program, which isn't in the cards. Hosting this as a webapp would also require rewriting the entire application.
The reason for this isn't that I didn't desire to support more systems, however I ditched my attempts to write it in java very early (long before full AMF support), and instead modified CoCEd which was already very mature. This saved weeks of development time and got an editor out to people very quickly.