I know of YaCy. It's written in Java which I'm almost completely unfamiliar with. But I know and follow the YaCy-community. Like myself the lead person of YaCy

I know of YaCy. It's written in Java which I'm almost completely unfamiliar with. But I know and follow the YaCy-community. Like myself the lead person of YaCy is located in Germany. We even share the same first name. :)