An overlay lets you show a call-to-action on top of the page your link points to, without leaving that page. Visitors still see the real destination in the background, but a popup appears asking them to do something first.
You can choose from six overlay types: a contact form, a quick poll, a custom message with a button, an email capture form, a clickable image/logo, or a coupon code with one-click copy. You pick which corner it appears in, and it attaches directly to any link you already have.