The most popular web server software in the world. Available for a wide variety of platforms. One of the first proof-of-concept open source projects along with Linux, BSD and Perl, Apache is far more secure than Microsoft's Internet Information Server (IIS) and has a wide variety of applications. Based on NCSA HTTPd as a patch thus called 'a patchie'.
The annual conference of all things Apache is ApacheCon - has it's own wiki: http://apachecon.com/wiki/
- OpenSourceHowTo.Org - Apache Setup Apache with OpenLDAP Authentication, OpenSSL, Access to Home Directories, Virtual Hosts, User access to their own home directories via webdav and openldap authentication, htpasswd & mod_authz_owner & with Webdav & htpasswd using openSSL certs
- Unofficial Apache Forum hosted by Nabble, currently archiving all the Apache projects' mailing lists to allow cross search and browsing. It has a fairly complete list of current Apache projects. You can drill into each project or search by keyword and observe the ongoing discussions.