In Google I / O, the annual event for company developers in San Francisco, was announced the next edition of Android M. Android M will be available for the public with compatibles Appliances in Q3 2015, however, you can download it and start building your apps now.
The company has already made available the system images for Nexus 5, Nexus 6, Nexus 9, and Nexus devices Player to the developers. If you are interested you can download Android M Developer Preview from the link below.
Developer.android.com/preview/index.html