These quick widgets are easy to add (via copy+pasting code) and can really help you engage visitors better.
OLark - free online chat software - pops up in the corner of your browser.
Efficient customer service - right on your home page.
Drip - automate email marketing compains - pops up in the corner of your browser.
Ever seen those "sign up now for our online course on [x]," and then wonder how they end up doing that? Drip is one of the easiest ways to do this.
Hello Bar - online bar at the top of a website that gets users to take action (e.g. email for an eBook).