[lch]

If it's written in something other than what the Mono Project supports (Microsoft's SharpDevelop) then you need to compile the programs under/for the target platforms. An EXE is Windows-specific and Windows-only. YaBasic is GPL software and there exist Linux versions of it, but you'll still need to compile the program into a Linux ELF file for Linux people to use. I haven't found any mention of a native Macintosh version of YaBasic, though, so you'll need to use something like DarwinPorts to install it. Or you could release the source code so that the users can take care of that themselves.