Check out the book Traction, to get a bunch of free marketing channels and a strategy. My favorite is to go after the bloggers that are read by your target customer community.

https://www.amazon.com/Traction-Startup-Achieve-Explosive-Cu...

Thank you, and because you named traction, I remember the book from DDG's founder Gabriel Weinberg [1], that was previous to his success.

[1] https://www.amazon.com/Traction-Startup-Achieve-Explosive-Cu...

Everything by Patio11 [0]. Traction by Gabriel Weinberg [1]. Also, see IndieHackers community [2] if you are interested bootstrapping.

[0] https://news.ycombinator.com/threads?id=patio11

[1] https://www.amazon.com/Traction-Startup-Achieve-Explosive-Cu...

[2] https://www.indiehackers.com/

This is the one that's usually recommended here. It's a great book! https://www.amazon.com/Traction-Startup-Achieve-Explosive-Cu...

Have you read the book Traction yet? It provides a very usable growth framework. More importantly, It also allows you to start thinking of marketing as a testable iterative process, and this simple change in mindset can do wonders for the engineer/hacker.

https://www.amazon.com/gp/product/1591848369/ref=as_li_tl?ie...

The website that goes along with the book https://www.amazon.com/Traction-Startup-Achieve-Explosive-Cu...

There are tons of different ways to market your side project and what works for someone else may not work for you, of course.

I think it really just comes down to where your potential customers may be hanging out / searching. For my side project, I've had decent success responding to posts/questions on sites like Quora, where someone is looking for exactly what you offer. It's free too (besides for your time!).

The book Traction (https://www.amazon.com/Traction-Startup-Achieve-Explosive-Cu...) gives a pretty solid overview of different marketing methods/strategies.