Smallchat Beta - Slack integration for chatting with visitors to your website
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Talkus - Chat with your website users from Slack
Firehose Chat - firehosechat.com
Zopim - Live chat is a faster and more personal way for you to engage your customers. Free for 14 days. No credit card required.
Speaklyn - Website visitors chat with you on Facebook Messenger