ImageMagick
As of version 4.2.4, ImageMagick supports MNG-LC and MNG-VLC,
and can convert most GIFs to MNG-LC files.
Get ImageMagick from
ftp://ftp.wizards.dupont.com/pub/ImageMagick/
or one of its mirrors, which are listed at
http://www.wizards.dupont.com/cristy/www/archives.html