Lepton can be built and run on many Linux and *nix systems as well as on MS Win under Cygwin and on Mac. As of now, there are some troubles with building it on the latter though you can install a virtual machine with some Linux OS, e.g., Ubuntu, and install it there.
The Lepton EDA Portability wiki page contains an incomplete list of systems on which you can install Lepton either from scratch, or using the system’s package manager, as well as some recipes on how to do it.
Here is probably an incomplete list of links to packages existing for various operating systems:
lepton-eda package maintained by Bdale Garbee
lepton-eda port by dmn
lepton-eda port by dmn
lepton-eda build by dmn
lepton-eda ebuild by Dominique Michel
lepton-eda spec by dmn
lepton-eda and lepton-eda with gtk3 support by Ian Glen
Please see this article initially contributed by Mario Giovinazzo on how to install Lepton on Cygwin.