Splitstack is the easiest way to do server-side AB tests on your landing pages. Server-side allows you to run experiments that have higher impact on your bottom-line, like completely different designs of your landing pages or different check-out flows, not just button colors or copy (something that you can't do with the majority of tools out there, which work client-side).

Server-side means also other befefits: better UX for your clients (faster uploading time of your page, especially on mobile devices), no "flicker effects". You can have your first experiment live after MINUTES from sign-up.