Apache Web Server
The Apache HTTPd Server, called simply Apache, is a free and open-source cross-platform web server software, released under the terms of Apache License 2.0. Apache Web Server is developed and maintained by an open community of developers under the auspices of the Apache Software Foundation. The Apache HTTP Server Project is an effort to develop and maintain an open-source HTTP server for modern operating systems including UNIX and Windows. The goal of this project is to provide a secure, efficient and extensible server that provides HTTP services in sync with the current HTTP standards.
HAProxy Load Balancer
HAProxy, which stands for High Availability Proxy, is a popular open source software TCP/HTTP Load Balancer and proxying solution. HAProxy is free, open source software that provides a high availability load balancer and proxy server for TCP and HTTP-based applications that spreads requests across multiple servers. It is a TCP/HTTP reverse proxy which is particularly suited for high availability environments. It features connection persistence through HTTP cookies, load balancing, header addition, modification, deletion both ways. It has request blocking capabilities and provides interface to display server status.
Bind DNS Server
BIND is an open source implementation of the Domain Name System (DNS) of the Internet maintained by ISC (Internet Systems Consortium). BIND 9 is intended to be fully compliant with the IETF DNS standards and draft standards. Important features of BIND 9 include: TSIG, nsupdate, IPv6, RNDC (remote name daemon control), views, multiprocessor support, Response Rate Limiting (RRL), DNSSEC, and broad portability. RNDC enables remote configuration updates, using a shared secret to provide encryption for local and remote terminals during each session.
OpenSMTPD Mail Server
OpenSMTPD is a FREE implementation of the server-side SMTP protocol as defined by RFC 5321, with some additional standard extensions. It allows ordinary machines to exchange emails with other systems speaking the SMTP protocol. Started out of dissatisfaction with other implementations, OpenSMTPD is a fairly complete SMTP implementation.
Dovecot IMAP4 Server
Dovecot is an open source IMAP4 and POP3 email server for Linux/UNIX-like systems, written with security primarily in mind. It is an excellent choice for both small and large installations. It's fast, simple to set up, requires no special administration and it uses very little memory. Supports both: the standard mbox and Maildir formats.