Onesheet CRM - The Simple CRM for Google Sheets
Laytr - Laytr is the easiest way to defer emails.
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.
FollowUpThen - The simplest way to schedule an email reminder
Freshsales CRM - A full-fledged CRM for high-velocity sales teams.
NudgeMail - Write or Forward any email to NudgeMail.