Asterisk is a hybrid TDM and packet voice PBX (Private Branch eXchange) and IVR platform with ACD functionality. It acts as middleware between the Internet (IAX, SIP, MGCP, Skinny, H.323), telephony channels (like Zaptel, T1, PRI, E1, FXO, FXS, VoIP, VoFR, ISDN, modems, Internet Phone Jack, etc.), and applications (like voice-mail, conferencing, directories, MP3 players, intercoms, etc.). It has many advanced features such as a codec translation API. The base distribution includes several channel backends, as well as applications. However, the beauty of Asterisk is its ability to be extended using its APIs, dynamic module loader, and AGI scripting interface. End users can even write their own applications that run on the system in C or any scripting language of their choice.
Clustering is the idea of making several computers act as one for the purposes of either performance or reliability. The Clustering Daemon guarantees that a response will be serviced provided at least one cluster node is up. It runs as a userspace process and provides a large amount of flexibility.
ClusterNFS is a set of patches for the "Universal NFS Daemon" (UNFSD) to allow multiple clients to nfs mount the same root filesystem by providing "tagged" filenames. When a client requests the file "/path/filename", the ClusterNFS server checks for the existence of files of the form "/path/filename$$TAG=value$$". If such a file exists and the client has a matching value for KEY, this file is returned. If the client does not have a matching value or no such file exists, the file request proceeds as normal. Currently supported keys include HOST (hostname), IP (IP number), CLIENT (matches any nfs client) and CREATE (for "tagged" creation of files).
Condor is a high throughput system, scheduling and providing large amounts of computational power over a long period of time. It provides the efficient use of a large variety of systems, from idle desktop workstations and dedicated clusters to grid systems all over the world, while its incredibly flexible configuration implements and maintains the machine owner's desired policy for the machine's availability.
The ENBD (Enhanced Network Block Device) is an industrial-strength version of the Linux kernel NBD. It makes a remote disk look like a local block device, allowing cheap and safe realtime mirrors to be built over the net. It features internal block-journalling and multichannel failover.
esky is an implementation of job freezing (checkpoint/resume) for Unix processes. It can save the state of a running process to disk then later resume it from the point it left off, possibly on a different machine. esky currently works on a limited but non-trivial range of processes. esky can cope with programs that open or mmap() files, including opening shared libraries with dlopen(). esky is implemented entirely in userspace - no kernel patches or modules are required. It works under Linux 2.2 and Solaris 2.6 and is written to be independent of CPU type.