Startup founders and business owners: what AI tool became a must-have for you?

I’m curious what AI tools are actually useful for running a small business or startup.

Not just the popular ones, but the tools that really save time, reduce manual work, or help you make better decisions.

For example: writing, research, customer support, content planning, sales, automation, reporting, design, or admin work.

What AI tool is now a must-have in your workflow, and what tool sounded useful but ended up being a waste of time?