Update to my earlier review:
Version 1.4 of scroll triggered box released today. It now supports Gravity Forms shortcodes and integrates to any email solution that GF supports (Constant Contact, Aweber...). v1.4 also negates my comment about no recent releases. I tested 1.4 and the GF shortcode in place of the default form markup worked great. Kudos to pk2000.
I read the 3 reviews here that weren't 5 stars - one of them from Joost who carries a lot of weight in SEO land - and so initially installed another scroll triggered box plugin instead of this one.
That was a mistake. It cost me a lot of time and troubleshooting before I circled back to this one. I was blown away when I finally tried it that the plugin was so insanely easy to install and get running - under 5 minutes in my case - and it came styled beautifully out of the box. I'm a front end developer who styles for a living - but this plugin saved me that time.
This is a free plugin with no premium version that I can see, so what you get is what you have. There's no integration to the typical email solutions: aweber, constant contact, mailchimp and emails aren't saved in the database. Also, there hasn't been a new release in some time.
In case you're interested in what happened with the other plugin - the one I gave up on... First there were conflicts with some other plugins on the install, which was causing the scroll triggered boxes (stb) config settings not to save. A workaround was to disable all other plugins, configure stb, then reactivate the others again. That works ok in a development environment, but not so well in production.
The other issue with stb was this "Warning: Invalid argument supplied for foreach() in .../plugins/scroll-triggered-boxes/includes/class-public.php on line 38". The dev, Danny Van Kooten, is a cool guy and responsive considering its a free plugin, but in this case it just wasn't an important enough part of the scope to continue working through all the issues.
The install I'm working on is hosted by WPEngine - which uses both Apache and nginx - and maybe if it were running on nginx I'd have had a problem like the others, but less than 15% of sites use nginx, so most won't need to worry about it.