Debian GNU/Linux -- All of Debian's free 3.0 and 3.0r1 distributions support IA 64, SPARC 64, Alpha, HP PC-RISC, MIPS, PowerPC, andIBM S/390. Two more versions are currently in the testing stage.
FreeBSD -- The newest version, FreeBSD 5, supports the DEC Alpha, SPARC 64. and IA 64 architectures. FreeBDS 5.1 has a port for AMD 64 chips.
Gentoo -- Gentoo now has ports to IA64, Alpha, and SPARC 64 chips.
Mandrake -- Mandrake Linux 9.0 for AMD 64 was released last March; pre-orders for Mandrake 9.2 ($199 US for the basic version) are now being taken. The enterprise server OS includes a high-performance Web server, FTP server, extended security services, and databases. Pricing: Sold under a subscription basis, which includes the product, support and direct access to software updates. Two support options are available: "Standard" ($749 USD) is valid for five incidents within a one-year period, and the "Unlimited" ($1499 USD) is valid for unlimited incidents during a one-year period.
NetBSD -- NetBSD/alpha is a true 64-bit system that fully implements the LP64 architecture, using 64-bit pointers and 64-bit long integers (standard integers are still 32 bits) in a linear, 4 TB address space. NetBSD/alpha was the first free OS to run on Alpha and supports the largest number of Alpha system types of any free OS. Version 1.6.1 was released last April. NetBSD also runs on AMD64, SPRAC64, MIPS64, and others.
OpenBSD -- Runs on Sparc64 and Alpha.
Red Hat -- Enterprise Linux AS ($2499 Premium Edition, x86, $1499 Standard Edition, x86) and Enterprise Linux WS ($299 Premium Edition, x86, $179 Standard Edition, x86). AS is designed for industrial-strength departmental and datacenter server deployments. WS is Red Hat's desktop/client partner for Enterprise Linux AS and Enterprise Linux ES. Red Hat's 64-bit MIPS Core Processor Toolkit has been available since August 2001. Red Hat for the new AMD 64 chips is due out in a few weeks.
SuSE -- SLES 7 for IBM zSeries is now available; beta and evaluation downloads are also available now. SuSE Linux 9.0 supports AMD 64. A boxed version of SuSE Enterprise Server for IBM for AMD 64 is also available, but only in Germany at the moment. Pricing: $598 (minimum 5 workstations). Here is a NewsForge review of SLES 8.0 for AMD 64 and a DevChannel review of SLES 8.0 for Itanium, both by Russell Pavlicek.
Turbolinux -- TurboLinux 8 for AMD 64 allows the use of existing x86 software infrastructure, enabling migration from 32-bit to 64-bit. Pricing: $99 with support (boxed); $69 without support (boxed).
We hope that this collection makes it convenient for you to compare a number of the 64-bit releases. Thanks to those readers who jumped on us immediately with some distros we missed the first time. Let us know about others, and we'll keep adding to the list.