Texted.io is the easiest way to send SMS messages to groups, and manage replies individually.
Textedly is an awesome SMS Marketing platform that enables marketers to build any type of text messaging campaign.
Harry is a tool to schedule SMS to attendees before or after an event on Eventbrite. This tool was made to communicate important information and remind people about events.
Slack Mass Direct Messages is a Google Chrome extension that allows Slack Admins to send direct messages to their people in bulk. This is not something one should do often, but every now and again, it can be a god send.