NetHunt CRM - Turn Gmail into a smart CRM
Onesheet CRM - The Simple CRM for Google Sheets
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Followup.cc - FollowUp for email is a lightweight productivity suite that keeps your conversations and tasks from slipping through the cracks. Set perfectly timed reminders that arrive at the top of your inbox, right when you need them.
Inbox by Reply - Handle your hot sales emails faster
Freshsales CRM - A full-fledged CRM for high-velocity sales teams.