Windows Live Wave 4 has been in the making for quite sometime now and should be released shortly, however, few MVPs and Microsoft Connect users got early access to the closed beta preview of Windows Live Wave 4.
However, like every software, a version of Windows Live wave 4 was leaked on the internet, and according to DSQ is also available for download through torrents.
Windows Live Wave 4 contains the same family of products from Wave 3 including Windows Live Mail, Live Writer, Live Messenger, Live Photo Gallery, Live Movie Maker and Live Sync among others. The Windows Live Messenger does not work right now for regular users, but there is a patch floating around the internet which will allow users to sign in using regular hotmail/live IDs.
Other changes in WL Wave 4 include a new ribbon interface for Windows Live Writer, and a Outlook like UI for Windows Live Mail.
Manan has been able to put up a detailed review of Windows Live Writer and Windows Live Mail which are part of the Wave 4 family, you might want to check it to see the new features and improvements in this version.
Wave 4 might be released as a public beta in the next weeks, however, leaked copies of the version are doing the rounds of the internet, you might want to check torrent search sites to download a version.