http://mat.i2p/metasearch
The main things I took from it were how result engines are shown in the search page and its ranking algorithm.
However, as mentioned previously, it’s slow and not as hackable as their readme would like you to think.
The (probably) second most well- known metasearch engine is Kagi , which sources its results from its own crawler, Google, Yandex, Mojeek, Marginalia Search, and Brave (I’ll talk about these search engines later).