The whole language, and most of the standard library are supported.
The compiler is easy to install: it only depends on Findlib and Lwt.
The generated code is independant of Eliom and the Ocsigen server. You can use it with any Web server.
You can use a standard installation of OCaml to compile your programs. In particular, you do not have to recompile a library to use it with Js_of_ocaml.
You just have to link your program with a specific library to interface with the browser APIs.