This article is from the CD-Recordable FAQ, by Andy McFadden (email@example.com) with numerous contributions by others.
CD-MRW is the working name for a CD-RW storage format developed by the Mount
Rainier Working Group (http://www.mt-rainier.org/). The Mount Rainier group
has creating specifications for native OS support of CD-RW and DVD+RW, with
the eventual goal of replacing floppies and similar formats (e.g. Zip disks).
EasyWrite is a marketing logo for Mount Rainier compliant drives. Drives
may be sold with the logo if they pass compliance and robustness tests.
This standard is being promoted by Compaq, Microsoft, Philips, and Sony.
The web site claims support by "over 40 industry leaders", including OS
vendors and PC OEMs.
What this means to you: 500+MB of reasonably fast storage that doesn't
require long formatting delays or the installation of special software.
Discs created with Mount Rainier appear to organize the data slightly
differently from other UDF solutions, so some compatibility problems exist.