swaks - Swiss Army Knife SMTP; Command line SMTP testing, including TLS and AUTH.

Highly recommended. Very useful. 

http://jetmore.org/john/code/ 

Robtex swiss army knife internet tool

Checks multiple RBLs. Check if your mailserver is listed in any blacklist

http://www.robtex.com/ 

Begin enjoying the benefits of server virtualization with the free VMware Server.

VMware Server installs on any existing server hardware and partitions a physical server into multiple virtual machines by abstracting processor, memory, storage and networking resources, giving you greater hardware utilization and flexibility.

Streamline software development and testing and simplify server provisioning as you utilize the ability to "build once, deploy many times."

http://www.vmware.com/products/server/ 

QEMU is a generic and open source machine emulator and virtualizer.

When used as a machine emulator, QEMU can run OSes and programs made for one machine (e.g. an ARM board) on a different machine (e.g. your own PC). By using dynamic translation, it achieves very good performances.

When used as a virtualizer, QEMU achieves near native performances by executing the guest code directly on the host CPU. A host driver called the QEMU accelerator (also known as KQEMU) is needed in this case. The virtualizer mode requires that both the host and guest machine use x86 compatible processors.

http://fabrice.bellard.free.fr/qemu/ 

Imapsync is a tool for facilitating incremental recursive IMAP transfers from one mailbox to another. It is useful for mailbox migration, and reduces the amount of data transferred by only copying messages that are not present on both servers.

Read, unread, and deleted flags are preserved, and the process can be stopped and resumed. The original messages can optionally be deleted after a successful transfer. 

http://freshmeat.net/projects/imapsync/ 

EtherApe is a graphical network monitor for Unix modeled after etherman. Featuring link layer, ip and TCP modes, it displays network activity graphically. Hosts and links change in size with traffic. Color coded protocols display.

It supports Ethernet, FDDI, Token Ring, ISDN, PPP and SLIP devices. It can filter traffic to be shown, and can read traffic from a file as well as live from the network.

http://etherape.sourceforge.net/ 

Ubuntu is a complete Linux-based operating system, freely available with both community and professional support. It is developed by a large community and we invite you to participate too!

The Ubuntu community is built on the ideas enshrined in the Ubuntu Philosophy: that software should be available free of charge, that software tools should be usable by people in their local language and despite any disabilities, and that people should have the freedom to customise and alter their software in whatever way they see fit.

http://www.ubuntu.com/ 

Puppy Linux, your complete, up-to-date desktop suite in 28-70 MB

Enjoy the speed of Puppy as a live CD, or better still, as multi-session CD or DVD in your CD/DVD writer.

http://www.puppylinux.org/ 

Only one remote hole in the default install, in more than 10 years!

The OpenBSD project produces a FREE, multi-platform 4.4BSD-based UNIX-like operating system. Our efforts emphasize portability, standardization, correctness, proactive security and integrated cryptography. OpenBSD supports binary emulation of most programs from SVR4 (Solaris), FreeBSD, Linux, BSD/OS, SunOS and HP-UX. 

http://www.openbsd.org/ 

Debian is a free operating system (OS) for your computer. An operating system is the set of basic programs and utilities that make your computer run. Debian uses the Linux kernel (the core of an operating system), but most of the basic OS tools come from the GNU project; hence the name GNU/Linux.

Debian GNU/Linux provides more than a pure OS: it comes with over 15490 packages, precompiled software bundled up in a nice format for easy installation on your machine.

http://www.debian.org/ 

CentOS is an Enterprise-class Linux Distribution derived from sources freely provided to the public by a prominent North American Enterprise Linux vendor.  CentOS conforms fully with the upstream vendors redistribution policy and aims to be 100% binary compatible. (CentOS mainly changes packages to remove upstream vendor branding and artwork.)  CentOS is free. CentOS is now accepting donations via PayPal, please click the button for more information.

CentOS is developed by a small but growing team of core developers.  In turn the core developers are supported by an active user community including system administrators, network administrators, enterprise users, managers, core Linux contributors and Linux enthusiasts from around the world.

http://www.centos.org/ 

Three-time winner of LinuxWorld Best in Show

Scalix Collaboration Platform named "Best Messaging Solution" three times by LinuxWorld Product Excellence Awards.

Scalix messaging products dramatically reduce your total cost of ownership. Our Linux-based Collaboration Platform gives you 99.999% availability with clustering and failover. Our message store uses a native Linux file system which is rock solid and eliminates the need for you to manage a database. Our Mail Server typically supports 50%-100% more users per server than Exchange, so you can consolidate servers. With our SmartCache processing on local machines, you can centralize messaging servers and eliminate the complexity of managing distributed systems.

http://www.scalix.com 

Thinstation is a thin client Linux distribution that makes a PC a full-featured thin client supporting all major connectivity protocols: Citrix ICA, NoMachine NX, 2X ThinClient, MS Windows terminal services (RDP), Cendio ThinLinc, Tarantella, X, telnet, tn5250, VMS term and SSH.

No special configuration of the application servers is needed to use Thinstation!

Thinstation can be booted from network (e.g. diskless) using Etherboot/PXE or from a local floppy/CD/HD/flash-disk. The thin client configuration can be centralized to simplify management.

http://thinstation.sourceforge.net 

The Network Box is the ultimate network security solution for small and medium sized enterprises.

Our award-winning network security package ensures you have the very best protection for your network at all times. The Network Box is a complete Unified Threat Management appliance that includes all the essential components required for computer security (firewall, intrusion detection and prevention, anti-virus, anti-spam, virtual private networking, content filtering) - at an affordable price.

With Network Box you are fully protected 24 x 7. Our Data Centres constantly monitor the Internet for new threats, remotely downloading protection onto your own Network Box using our unique 'global push' technology - automatically ensuring your network is totally secure at all times.

http://www.network-box.co.uk/ 

IPCop Linux is a complete Linux Distribution whose sole purpose is to protect the networks it is installed on. By implementing existing technology, outstanding new technology and secure programming practices IPCop is the Linux Distribution for those wanting to keep their computers/networks safe.

The IPCop Linux Team is dedicated to doing the very best job possible to keep your systems safe, as you can see on our site.

"The Bad Packets Stop Here!"

 http://www.ipcop.org

SmoothWall began as an open source firewall project, which now protects a million networks worldwide.

The SmoothWall company produces firewall, web security/content filtering, email security/anti-spam and bandwidth management (QoS) products with commercial support.

http://www.smoothwall.co.uk/ 

Eximstate is a web based queue monitoring tool written by Ollie Cook.