The GNU Gatekeeper is a free H.323 gatekeeper based on the OpenH323 project. You can use it to manage a Voice-over-IP network and let endpoints (e.g., Netmeeting) communicate through symbolic names. It also has an external interface for billing and other applications. It runs on a number of Unix versions (including Linux and Solaris) and Windows.
Kamailio (formerly OpenSER) is a high-performance SIP (RFC3261) server with a flexible architecture and many extensions. The server implements proxy, registrar, redirect, and location SIP/VoIP services. It has support for UDP, TCP, TLS, and SCTP transport layers, ENUM, AAA via database, RADIUS, DIAMETER, gateways to SMS and XMPP, least cost routing, load balancing, NAT traversal, and call processing language. Kamailio implements SIMPLE presence and instant messaging extensions, and includes an embedded XCAP server and MSRP relay. It can be also used as a routing SIP sever for WebRTC via WebSocket.
msmtp is an SMTP client with a sendmail compatible interface. It can be used with Mutt and other MUAs. It forwards messages to an SMTP server which does the delivery. Features include various SMTP AUTH methods, TLS/SSL-encrypted connections (including support for client certificates), support for multiple accounts, DSN, and IPv6 support.
aria2 is a utility for downloading files. The supported protocols are HTTP(S), FTP, BitTorrent, and Metalink. It has a powerful segmented downloading ability, downloading a file from multiple sources and multiple protocols and utilizing your download bandwidth to the maximum. It supports downloading a file from HTTP(S)/FTP and BitTorrent at the same time, while the data downloaded from HTTP(S)/FTP is uploaded to the BitTorrent swarm. Using Metalink's chunk checksums, aria2 automatically validates chunks of data while downloading a file like BitTorrent.
Cerb is a fast and flexible Web-based platform for business collaboration and automation. It helps you remember anything about anyone, collaborate from anywhere, deftly reply to a flood of email, automate, stay informed, capture feedback, track time, flag opportunities, manage tasks, share expert knowledge, and otherwise execute efficiently.
The WendzelNNTPd is an IPv6-ready Usenet server that aims to be as easy to use as possible. It is portable, supports AUTHINFO authentication, contains ACLs as well as role based ACLs (RBAC), supports invisible newsgroups, and features automatic prevention of double postings. WendzelNNTPd supports MySQL as well as SQlite3 backends.