There is only one file type that uses the .OTLN extension:
Opal Outline File
Outline created by Opal, an outlining program for Mac OS X; creates hierarchical lists for organizing notes, projects, reports, ideas, etc.; Opal is the successor to Acta and has been completely rewritten for Mac OS X.
More information is available at the Opal Product Page.
|A Sharp Opal|
Updated: February 13, 2007