Lightbox.clone is a project mainly written in JavaScript, it's free.
Mootools lightbox clone
Single file lightbox
rel: 'lightbox',
speed: 300,
margin: 50,
resize: true,
overlay: false,
overlayOpacity: 0.8,
overlayColor: '#000',
onLoad: function(){},
onOpen: function(){},
onClose: function(){},
onZoomIn: function(){},
onZoomOut: function(){}