So far with Android M, there have been a number of new features and tweaks announced that promise to refine and enhance the user experience on Android. Control over the heads up notifications, the new Doze feature, and the customizable Quick Settings tiles are all little adjustments Google has made to the operating system which can be played with right now for users who have access to the developer preview. One feature which Google didn't talk about though is something which Android users have been requesting since Samsung introduced their version of it, a multi-window feature to allow a couple of open apps on the screen at the same time.
It should be noted that while Multi-Window seems to be included in the developer preview version of Android M, it's experimental and the final version of the OS release should have this feature fine-tuned to work much better. As this is something many Android users have been asking for though, it's nice to finally see Google implementing it into the OS as a native option. It's uncertain whether or not Multi-Window will make it into the final release of Android M when Google pushes it out later this Fall, but in all honesty there's a chance it could go either way.
As stated above, anyone using the Android M developer preview can access and play around with the Multi-Window feature, but know that this is not a simple process. It isn't like many of the other features you may have already seen in Android M which can be toggled on with the tap of a button. According to the Reddit thread where this feature was discovered, there is quite a few steps to go through before you can enable it. It also requires a bit of knowledge of using ADB, but if you were able to load on the developer preview of Android M in the first place you probably already have an understanding of ADB. You can find the instructions over at the Reddit thread if you want to give this a try. The good news is that once you enable it, disabling it is fairly easy and can be toggled off from developer options in the settings menu.