Where to run ads?

Hi all,

I run Daily Time Tracking, a time tracker for Mac that works by periodically asking what you are doing.

As I'm having a full-time job next to it, I need to pay quite some tax on my profit. Hence, I need to reduce it by making costs. I prefer having some ROI so thinking of running ads.

Users are working in a lot of different industries (IT, education, marketing, architecture, etc.) so hard to target that. Thinking of targeting the type of users typically relying on time tracking solutions: freelancers, consultants & agencies.

Also, the app is Mac-only, so I strongly prefer to only target users using Mac.

Where would you run ads to gain the most ROI?

Thanks!