Y&Y, Inc. closed in 2004. For volunteer support and continuing discussions regarding the company and fonts, please see the yandytex and lucida mailing lists (feel free to subscribe).
The Lucida fonts are available from TUG and Personal TeX; the latter also distributes the MathTime fonts.
Thanks to a very generous decision by Blenda Horn, TUG is able to provide the sources to the Y&Y system, licensed as free software under the GNU GPL, as the yytex project at Google Code. You can browse the sources online or download them with Subversion. Various Y&Y documentation and support files are also included, but no binaries. If you are a Windows programmer interested in reviving the distribution, please take a look.
These FAQ's and web pages are from the Y&Y web site, slightly modified.
TUG provides the sources and these pages as a service to the Y&Y user community. To support this and other TUG activities, please consider joining TUG.