TextBlast is perfect for SMS marketing and communication.
Send customized messages in 4 steps:
1. Write your message
2. Select your contacts
4. Send each message
Note that SMS are sent from your device at your own expense (depending on your network provider).
Textedly is an awesome SMS Marketing platform that enables marketers to build any type of text messaging campaign.
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.