Another borderless (or is it border-less?) XFWM4 theme, this one based on Linux Mint's awesome "Mint-Y" theme.
Since this theme is a borderless one, the usual recommendations for such themes apply, those are (IMHO):
Enable composite and use the drop shadow effect, and be aware that you more than likely will have to resize the windows either by extending (or reducing) those by the title bar, or using the Alt key + the mouse left button.
To install the theme (system wide) simply unzip and copy the "Mint-Y-Borderless" directory to /usr/share/themes/ and then select the "Mint-Y-Borderless" Window Manager theme selecting it on Settings > Window Manager.
This is a modification of a Linux Mint theme, so all credit goes to them, I just edit the original theme to make it borderless (or border-less ?)