OnePlus One tries app-only sales in India tomorrow
The homegrown OxygenOS, based on Android 5.0, has already started rolling out. CyanogenMod 12s, also based on Android 5.0, has been certified by OnePlus and should start getting pushed out in days.
Don't wait until the last minute if you are looking to make this purchase tomorrow. Download and install the Amazon app on your current device now so that you won't miss this opportunity to buy the OnePlus One without an invitation in India.