Previously I used free pr (it's not free because you invest your time) successfully, but wouldn't do it today. If you are with this project in the long run, I would do SEO (use tools like ahrefs): Find content that is relevant to your domain, look at sites who linked to that content and reach out to them offering them to link to your product or relevant blog post. FB, Insta, Reddit, HN, PH etc. are all places you can post your product once or twice. If you are testing the demand for your product, that might be enough (as long as your target market sees it). But if you are here for more than just testing, SEO is key imho. Good luck!
Mostly by writing a blog posts and driving SEO traffic. But this takes a long time and may not succeed unless your blog posts are discoverable. You solve this problem by writing guests on other people's blogs (usually blogs that are in your product's niche).
I have a side project where the content is automatically created (product descriptions), in addition there is some hand written content and we did some manual backlink building, both by finding places where you get backlinks such as forum profiles, and also asking people to backlink to us. 150 visits a week at the moment.<p>This may not be a good strategy for you, it depends what sort of audience you need.