NZBHydra2 is described as 'meta search for NZB indexers. It provides easy access to a number of raw and newznab based indexers. You can search all your indexers from one place and use it as indexer source for tools like Sonarr or CouchPotato' and is an app in the News & Books category. There are more than 10 alternatives to NZBHydra2 for a variety of platforms, including Online / Web-based, Self-Hosted solutions, Mac, Windows and Linux. The best alternative is SickChill, which is both free and Open Source. Other great apps like NZBHydra2 are Binsearch (Free Personal), NZBgeek (Freemium), drunkenslug.com (Free) and NZBScout (Free).
Spotweb is a decentralized usenet community based on the Spotnet protocol. Spotweb requires an operational webserver with PHP5 installed, it uses either an MySQL or an PostgreSQL database to store it's contents in.
nZEDb is a newsgroups indexer. nZEDb automatically scans usenet, similar to the way google search bots scan the internet. It provides a web-based front-end providing search, browse, and programmable (API) functionality.
Usenet indexer to find and download nzb files throw a modern webbased app with lots of preview material for certain categories. The service helps you to search through usenet newsgroups and download available content even if it was obfuscated.