J7Z runs on Windows (XP+), OS X (v10.8+) and Linux (v2+).
It depends on P7Zip v9 (in OS X and Linux).
It needs the Java Runtime Environment (JRE) v1.7 or newer.
Installers can be downloaded from the SourceForge website.
Download each desired skin's JAR file into J7Z's "Lib" folder.
Alternatively, specify another location via the External menu's "Lib-Dirs" entry.