Text, email, and tweet to make stuff happen. Apps without an interface are on the rise. Some useful ones:

☎️ Call Frank every night to record feedback on your day
🤖 Taylor is your personal travel assistant that tells you where to go
💰 Digit is an SMS bot that monitors your bank account
👔 Peter is your AI-based business lawyer
💬 Assist brings your favorite services directly to your messaging app
💌 The Simple Postcard lets you text a photo to mail it as a postcard

For more Invisible Apps check out the full collection on Product Hunt.