The long-rumored Android M has been introduced at the Google I/O 2015 conference and the release date of the OS is expected to be in the third quarter of this year. Also, Google has released the Android M developer preview for a slew of devices.
The Android M developer preview is available for these devices: LG Nexus 5, Motorola Nexus 6, HTC Nexus 9 and Asus Nexus Player.
GSM Arena says that in order to flash the Android M developer preview, users may have to unlock the bootloader of the handset and this process apparently erases all the saved data on it. Meanwhile, here is the link to the preview SDK.