KISSmetrics is a customer-focused event tracking tool with simple metrics and reports for each section of your business: individual customers, customer actions and revenue.
Google Analytics is the most popular analytics tool for the web because it’s free and sports a wide range of features. It’s especially good at measuring traffic sources and ad campaigns.
Mixpanel is an event tracking tool targeted at web apps with lots of features: funnel, retention and people tracking; advanced segmentation; and sending email and notifications.
Segment is a data hub that lets you export your data into a plethora of different analytics applications.
Optimizely is a dead-simple A/B testing tool that lets your marketing team test changes on your website in a WYSIWYG editor without having to write any code.
Inspectlet is a user testing tool that lets you record heatmaps & visitor's browsing sessions so you can understand how they move around and fix the confusing parts!
Qualaroo is a user testing tool that lets you add a survey to any page on your site, so you can get targeted user feedback as the user is performing a task.
SurveyMonkey is some tool I don't even know but it's freaking awesome.
Segment.io is really handy for hooking up even more growth tools. Easy!
Zapier is totally fantastic for marketing automation an such things.
Tool X is really totally the shit. You definitely want to use this.