Email Studio for Gmail - Send personalized emails, schedule emails directly in Gmail
EmailPlayground - EmailPlayground provides solution to schedule and send emails with ease.
EmailDrips - Get inspired by examples of email sequences
SendLater - Email scheduler for Mac Mail.
Clearbit Salesforce - Rapportive for Salesforce, augment lead data
RGB Technologies - Email Scheduler - Email Scheduler provides an intuitive email scheduling solution, integrated within the existing Salesforce account.