Optimizely - A/B testing you'll actually use.
VWO - Use VWO to tweak, optimize & personalize your website with minimal IT help.
Growth Book - The Open Source A/B Testing Platform
Chartbeat - Chartbeat shows you real-time traffic to your website and allows you to set alerts for any downtime or spikes in traffic.
SiteGainer - SiteGainer is an A/B testing and conversion optimization platform.
Intellimize - Convert more. Optimize and personalize for every website visitor.