SaluSafe is an encrypted email, chat, and file storage and sharing system. Your email and files are highly encrypted end-to-end, and cannot be intercepted by any third party. It was built from the ground up for security via strong cryptography, and is not just another security wrapper on top of an existing email solution.
PerlShare is a DropBox drop-in to create your own private file sharing "cloud". It consists of two parts; a client and a server. The server part lets you configure a Linux machine to accept PerlShare clients. PerlShare behaves a lot like DropBox. On collisions, for example, it creates conflicted copies. The workhorse for synchronization is Unison, a very reliable piece of software from Pascal Bach.
PeerProject is a versatile peer-to-peer filesharing client and file manager. It's intuitive and aesthetic while supporting many networks and features, including BitTorrent, G2, Gnutella, eDonkey, DC++, IRC, HTTP/FTP, and more. It's a mainstream fork of Shareaza p2p, for Windows and WINE.
Image Tools is a screen capture and file sharing tool. It features multi-threaded batch image resizing, conversion, cropping, flipping/rotating, watermarks, decolorizing (grayscale, negative, sepia), and optimizing. The BMP, GIF, TIFF, JPEG, PNG, and EMF image types are supported. It is compatible with MONO (only for GNOME). Multicore processing is supported to increase performance. The quality for output when optimizing is variable. Color channels can be filtered. An internal benchmarking tool is available. Indexed pixel format images can be processed.
KTorrent is a BitTorrent application that allows you to download and share files using the BitTorrent protocol. Key features include queuing of torrents, global and per-torrent speed limits, previewing of certain file types, importing of partially or fully downloaded files, file prioritization for multi-file torrents, selective downloading for multi-file torrents, kick/ban peers with an additional IP Filter dialog for list/edit purposes, UDP tracker support, support for private trackers and torrents, support for µTorrent's peer exchange, support for protocol encryption (compatible with Azureus), support for creating tracker-less torrents, support for distributed hash tables (DHT), support for UPnP to automatically forward ports on a LAN with dynamic assigned hosts, support for webseeds, scripting support via Kross, and interprocess control via DBus interface.
Forban is a P2P file sharing application for link-local and local area networks. Forban works independently from the Internet and uses only the local area capabilities to announce, discover, search, or share files. Forban relies on HTTP and is opportunistic, meaning that it replicates any files of interest seen in its proximity. The Forban protocols are minimalistic to ease the production of other implementations.
Although widely used, currently popular peer-to-peer (P2P) applications offer no user privacy. By design, services like BitTorrent and Gnutella share data with anyone that asks for it, allowing a third-party to systematically monitor user behavior. As a result, using a P2P network means that your online activities become public knowledge. OneSwarm is a peer-to-peer tool that provides users with explicit control over their privacy by letting them determine how data is shared. Instead of sharing data indiscriminately, data shared with OneSwarm can be made public, shared with friends, shared with some friends but not others, and so forth.