UrBackup is an efficient client/server backup system for Linux and Windows. A client for Windows lets you backup open files and complete partition images. Incremental and full image backups are stored to disk in a efficient way with file level de-duplication on either Windows or Linux servers. An easy-to-use server Web interface lets you analyze storage usage, view logs, modify settings, and browse backups. Backup images can be restored using a prebuilt live Linux CD based on KNOPPIX.
Aftpd is an FTP server for anonymous access designed for Unix-like operating systems. It uses an asynchronous model of connection processing and provides service for all users within a single process; can use multiple threads to run more efficiently on multi-core systems, with each thread serving multiple clients simultaneously; uses effective mechanisms of transferring files, minimizing copying of data in RAM (sendfile or a combination of the system calls mmap/writev); uses effective event notification schemes (kqueue on FreeBSD and epoll on Linux); uses poll or select in older systems; and supports IPv6. For safety, it works as an unprivileged user and uses chroot.
Syncless is an experimental, lightweight, non-blocking (asynchronous) client and server socket network communication library implemented in Stackless Python 2.6. It contains an asynchronous DNS resolver (using dnspython) and an HTTP server capable of serving WSGI applications. It aims to be a coroutine-based alternative of event-driven networking engines (such as Twisted and FriendFeed's Tornado). It is already about that fast, but it has fewer features and is less stable now.