konspire is a searchable, distributed file-sharing system featuring resumable file transfers and fast, exhaustive substring searches of all hosted file names on the network. konspire is written using pure Java. Load from processing search requests is distributed throughout a dynamically connected network of servers. Several fault-tolerant features ensure system correctness and reliability.
FemFind is a crawler and search engine for SMB shares (provided by Samba/Unix or Windows) and FTP servers. The crawler maps the filesystem structure of your shares to a MySQL database. Then, the Web interface or a Windows client can be used to quickly locate any file on the network.
Audiogalaxy's Satellite is a distributed music search agent. It is a small application which does mp3 searching and file transfer and makes a designated directory on your computer searchable by other Satellite users. It features a real-time transaction-based system for file sharing. The Linux version has no user interface, but files are selected via the Web for transfer from other users.