Not so long ago, in order to achieve such effects, we used JS. But, now, CSS3 has all the necessary tools for making pop-up windows too.
Singup / Login Forms PopUp windows No Javascript, only HTML and CSS Very Easy to costumize. Very Easy to Integrate & Use Modern Browser SupportSocial ButtonsPassword RecoveryError Handling State (requires javascript files)Help documentation
index.htmlstyle.csspagestyle.csshelp documentation.
Background from the preview is downloaded from subtlepatterns If you like, don’t forget to rate it!
ChangeLog 19/02/2013 – Version 1.1
Added password recovery Update video review and screenshots18/02/2013 – Version 1.0
Initial release