I'm not a fan of google but you can do exactly what this search engine does by curating your own list of domains to search against.
- search queries are performed directly from the clients computer so can't protect their privacy (since Custom Search JSON API have a daily limit of 10k queries)
- forced to use javascript, and the way it's implemented makes it difficult if not impossible to do even basic things like the loading animation cards
- ads are loaded from an iframe so you can't do any styling (except extremely limited options that they make available in their settings, but no matter what then it will be very ugly if you want to have a light/dark theme)
But there are of course many benefits as well, such as it being 'free' (Bing is ridiculously expensive IMO, and feels impossible to join their ad network to offset the costs.. which might explain why you see countless Bing proxies shut down after a few months) and search results are no doubt better than the ones you'd get from Bing.
edit: Looks like this OSS project was launched and cancelled in a single day.
Touché :-)
However the idea of a federated search is some measure of protection against that. If it ever happens.
I can't tell whether this is a neglected Google product that they were going to refresh but lost interest in, or something that is undergoing a breath of fresh air.
As you say, I was able to add a list of domains and get some pretty decent results from it. The UI makes me feel like Google are not interested in making it a truly successful product, though.
Which raises the question: does archive.org offer their Wayback Machine index for download anywhere? Technically, why should anyone go through the trouble of crawling the web if archive.org has been doing it for years, and likely has one of the best indexes around? I've seen some 3rd-party downloaders for specific sites, but I'd like the full thing. Yes, I realize it's probably petabytes of data, but maybe it could be trimmed down to just the most recent crawls.
If there was a way of having that index locally, it would make a very powerful search engine with a tool like yours.