The best alternatives to Boomerang are Boomerang for Gmail, If No Reply, and Fridai. If these 3 options don't work for you, we've listed a few more alternatives below.
What do you think of Boomerang?
AssemblyAI— Speech-to-Text API with superhuman accuracy
If No Reply is the sales automation choice for small and medium sized businesses. It's easy to set up and simple to use while offering the flexibility to completely personalise every message.