Searx (as others have said) is an aggregate of multiple search engines all bundled into one, with very finetuned customization (ie: you can toggle every search option you want or not within each category).

You also don't need to host your own, though I'm not sure what the significance of being self hosted in this case is.

As far as usefulness over other search sites, it's generally better with some caveats. Search engines as a whole are in a pretty awful state, so combining them is better, but still not that good. It does offer some very niche search engines that can be extremely useful when pooled together though, which is nice.

Searx also has some captcha issues that I haven't quite figured out. My understanding is that essentially, search engines don't like when you use their engine without being on their site, and it'll stop working via searx (until you go to the site in question and do the captcha maybe?).

There's also a few different domains for searx with varying degrees of availability as far as what engines they reliably connect to.

All in all, searx is great by comparison to mainstream trash, but it can be a headache to setup, and a headache to maintain. There's a masterlist of searx hosts somewhere, I'll try and see about finding it if someone else doesn't link it.