SitePush is a WordPress plugin which allows you to have multiple versions of your WordPress site, so you can edit, develop, test without any risk to your main, live site. It's great for developers, designers and editors... anyone who wants to be able to test changes to a site before it is visible to the world.

For example:
you can easily move content between sites. For example, make extensive edits on a private staging site, and then push changes all at once to your live site. Or, easily pull copy of your live database into your development site so you are developing against the latest content.
test new themes and plugins, and only push them to your live site once they are configured and working as you want.
upgrade WordPress, themes and plugins on a private site so you can test that nothing breaks before upgrading your live site. Sure you take backups before any upgrades (right?), but it's a pain doing a full backup and an even bigger pain restoring from a backup.
easily make small (and big!) code changes on your development site, test and easily push new code to a live site. Great for dealing with clients who want "just one more thing".
Although SitePush installation is a bit more involved than a typical plugin, once set up it runs with minimal effort and can be easily used by non-tech authors & editors. Site admins can easily configure SitePush so that non-admins can only push content (i.e. posts/pages, comments and uploads) and to a restricted set of sites.

Please read the Installation instructions before you install SitePush - it's not a normal download and activate type of plugin installation.