What are your usage metrics? Especially your returning users. How long and regularly do your users get on the site?

If you don’t have regularly returning users and don’t plan on meaningfully changing the site, then I’d either sell ads or go build a related product/paid version and advertise it for free on this site.

How much traffic do you get on daily basis

Going through your site, and I’m not getting any monetization ideas.

If you have a competitor, could you check in on their work and how they monetize?

If you’re collaborating with others in the space, I’ll look at affiliates.

Or if you have lots of visitors, you can use an ad network.

By the way, I operate https://worqstrap.com/ and only monetizing through affiliates (it’s pretty hard).

What about implementing some Ad Sense ? :)