RedHat Linux, but designed for corporate scenarios. Released less often than RedHatLinux, kept more stable, supported to the Nth degree. If someone has certified their software for Linux, it's probably going to be on this.

http://www.redhat.com/software/rhel/

Red Hat Enterprise Linux products are delivered through an annual subscription with one year of support services and access to Red Hat Enterprise Network.

Comes in three flavours: AS (Advanced Server) for 4+ procs & clustering, ES (Enterprise Server) for 1-2 proc servers (this is probably the one you want for most cases), and WS (Workstation).

Is not available free, but is Free. (Yes, the GPL allows this.) If you get the CDs from someone with a subscription, and build the SRPMS yourself, it would seem you're allowed to have it.

Highlights

• Stability - 12-18 month release cycle and five years of support for every version.
• Performance - With multiple kernel performance enhancements and the audited industry-standard benchmark results to prove it.
• Manageability - Red Hat Enterprise Network is included. Provides industry-leading patch/security management and delivery, and optional system monitoring.
• Applications - Rapid adoption of the Red Hat Enterprise Linux family by ISVs means the applications you need to run your business, from vendors such as Oracle, VERITAS, BEA, CA, and IBM, are available and fully certified. Even better, because all Red Hat Enterprise Linux family members are based on the same core operating system foundation, when an application is certified on one family member it is automatically certified on them all.
• Certified hardware - Major hardware OEMs, including Dell, HP, and IBM, have certified their systems to run with Red Hat Enterprise Linux products.

Latest release at 16/8/03 is 2.1, but there's just been a beta called Taroon released.

An indepth discussion of what you can and cannot do with RedHatEnterpriseLinux is: Can I copy it?

How to rebuild RHEL from the source RPMs? (and Mailing List)

CategoryDistribution