OPML 2.0 draft spec (englisch)
Public review of OPML 2.0 draft spec.
http://www.opml.org/2006/03/04#a278

OPML 1.0 (englisch)
OPML 1.0 Specification. OPML is a format for storing outlines in XML 1.0 called Outline Processor Markup Language (OPML).
http://www.opml.org/spec

Share Your OPML (englisch)
Share Your OPML
http://share.opml.org/

Plain text to OPML Generator (englisch)
Plain text to OPML Generator
http://www.unold.dk/code/opmlgen/

MonitorThis (englisch)
With MonitorThis you can subscribe to 22 different search engine feeds at the same time. Enter a search term and click the 'make monitor.opml' button to get a list of rss feeds in OPML format.
http://alp-uckan.net/free/monitorthis/

optimalbrowser.com (englisch)
OPML Browser
http://www.optimalbrowser.com/

Yahoo Group - OPML developers discuss applications. (englisch)
Yahoo Group - OPML developers discuss applications.
http://tech.groups.yahoo.com/group/opml-dev/

OPML Validator (englisch)
OPML Validator
http://validator.opml.org/

Opmlmanager.com (englisch)
Opmlmanager is an online webservice that makes maintaining your own opml-file very easy. This opml-file can be a file that is part of a distributed directory, like the ipodder directory, a subscriptionlist, a readinglist, a file you use for taskable.com, etc. The outline-structure of your opml-file is represented in a foldertree that can be edited with a click of your mouse. You can easily add, edit and delete nodes and links.
http://www.opmlmanager.com/

Opmlworkstation.com (englisch)
Opml Workstation enables educators to create Web 2.0 team, course and community sites. OPML Workstation provides educators with the scope and flexibility to express their widest ranging and fastest-moving interests.
http://www.opmlworkstation.com/