Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
Novocall - Novocall converts web visitors into sales calls in seconds.
Freshdesk - Freshdesk is a cloud-based customer support software that lets you support customers through traditional channels like phone and email, social channels like Facebook and Twitter, and your own branded community
OptinMonster - OptinMonster helps to convert abandoning website visitors into subscribers and customers.
HelpScout - Help Scout is a simple, straightforward way to provide excellent support
Callpage - Turn website visitors into sales calls. Use CallPage and provide immediate free phone callback to your leads in 28 seconds.