Calendly - Say goodbye to phone and email tag for finding the perfect meeting time with Calendly. It's 100% free, super easy to use and you'll love our customer service.
Roundcube - Web-based IMAP email client
Acuity Scheduling - Automate your client bookings, cancellations, reminders & payments using the worlds friendliest online scheduling software.
HEY - Email at its best, new from Basecamp.
Doodle - Make meetings happen. With Doodle, scheduling becomes quick and easy.
Mailo - Mailo is an email client where you can send and receive emails to and from anyone with an email address.