Apache
More than 50% of all web servers are powered by Apache. Apache was created by a loose confederation called the Apache Group who started out with a few “patches” to the web server originally created at the National Center for Supercomputer Applications (NCSA–the same outfit that built the original Mosaic browser). They have created the dominant industry standard. An NT version is now available. Apache Server Project
The brain trust of the Apache community
C2NET Software
Most noted for their Stronghold Servers and full-strength encryption software.