S3cmd is available from SourceForge and GitHub
Download S3cmd From SourceForge
Download From SourceForge - Latest released version is 1.6.1
S3cmd requires Python 2.6 (or newer). S3cmd is not compatible with Python 3.x
See the INSTALL file contained in the download for installation instructions.
Download S3cmd From GitHub
GitHub is the preferred way to access all latest fixes that are not yet published on SourceForge.
Note for developers: if you are about to help with S3cmd development check out the source tree to your machine by forking it first in github, then checking out your personal fork, pushing changes back to branches in your personal fork, and filing pull requests on github.
S3cmd Linux Repositories
Linux repositories are available for some of the most popular Linux distributions on this page: