Microsoft has released a new video introducing Windows 10 as well as the Windows Insider program. Insider program opens tomorrow, as well as the download for the technical preview. As with previous tech previews – they are meant as beta software and not the final product (there were a lot of people thinking it was the final version when Win 8 was in preview).
They have also updated their Windows blog with an “Introduction to Windows 10” post as well, with more details – http://blogs.windows.com/bloggingwindows/2014/09/30/announcing-windows-10/