SL viewers not written in C++?

I suppose it depends on the exact meaning you're going to use for the term "non-trivial", but being fair and not using platform-specific capabilities/libraries/functions as a litmus (which even C/C++/Modula-3 will have problems with), yes, I can.

I have several programs written which compile on both Windows and Linux platforms that I would consider are "non-trivial" (a full DynDNS implementation, with protocol support for modification as well as a database), and I have older TurboPascal applications I wrote in the early 80s that will compile and run on FreePascal without modification, though they will sometimes require a platform-specific library (text screen handling and audio, mainly) to do so.

Delphi/Kylix only supports x86 code generation on Windows and Linux, but FreePascal is Delphi-compatible, and compiles to a wide array of platforms.

As such, I think it passes that litmus, at least for everything I have need to do with it.

this is without doubt the geekiest thread to ever exist in resident answers

Either you're defining things like "opening and reading files" as "platform specific", or FreePascal has to have a Turbo Pascal compatibility mode. Turbo Pascal was never compatible with any real Pascal that did anything more than read/readln and write/writeln to an already-opened file. Turbo Pascal was its own language, with its own I/O, its own linking/library model, and everything.