Antigen is described as 'small set of functions that help you easily manage your shell (zsh) plugins, called bundles. The concept is pretty much the same as bundles in a typical vim+pathogen setup. Antigen is to zsh, what Vundle is to vim'. There are five alternatives to Antigen for a variety of platforms, including Linux, Mac, zsh, BSD and fish. The best alternative is Oh My Zsh, which is both free and Open Source. Other great apps like Antigen are Prezto (Free, Open Source), Oh My Fish (Free, Open Source), zgen (Free, Open Source) and zplug (Free, Open Source).