I run an SEO agency, and thanks to Brexit i have put planned expansion on hold.

I'm looking for a way to do something productive with my time, because right now things are ticking over nice and steady. Clients are ranked and happy, and while my staff have work, i personally don't have much to do.

Before i got into SEO i was a developer, so im thinking of making a free version of a SEO tool to get back into coding this year.

Any recommendations? Which SEO tool do you hate paying for that has no free alternative available?

(Reasonable suggestions requested, don't go suggesting i make a free version of something on the scale of Majestic. I'm ok with renting a couple of servers if needed, but i'm not going to start scraping the entire web.)

I will share it on here for all to enjoy when complete.