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.
auto nice daemon activates itself in certain intervals, and renices jobs according to their priority, and CPU usage. Jobs owned by root are left alone. Jobs are never increased in their priority. It is very flexible. The renice intervals can be adjusted, as well as the default nice level, and the activation intervals. A priority database stores user/group/job tuples along with their renice values for three CPU usage time ranges. The strategy for searching the priority database can be configured. Linux, OpenBSD, FreeBSD, Digital UNIX, Solaris, and IRIX are supported.
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.
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.
distributed.net is a loosely knit group of computer users from all of the world that is taking up challenges requiring lots of computing power (most notably the RC5, DES, and OGR cracking contests). It is simple to participate in the challenges by downloading and running their client software (which uses idle CPU time to complete its tasks).
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.