Find RexTarget on GitHub (MIT license).
RexTarget manipulates the target attribute of your links on Redaxo websites when you add the Redaxo variable REX_YTILS_REX_TARGET to your templates.
You can define the manipulation behavior in the settings.
Ytils RexTarget is available on the Redaxo add-on installer. Click Installer on your Redaxo backend and then find the module with they key named ytils_rex_target. You can find RexTarget on GitHub as well.