Android O introduces a number of new features and APIs to use in your apps. Here's are just a few of those features;
Building on the work we began in Nougat, Android O puts a big priority on improving a user's battery life and the device's interactive performance. To make this possible, we've put additional automatic limits on what apps can do in the background, in three main areas: implicit broadcasts, background services, and location updates. These changes will make it easier to create apps that have minimal impact on a user's device and battery. Background limits represent a significant change in Android, so we want every developer to get familiar with them. Check out the documentation on background execution limits and background location limits for details.
Android O also introduces notification channels, which are new app-defined categories for notification content. Channels let developers give users fine-grained control over different kinds of notifications — users can block or change the behavior of each channel individually, rather than managing all of the app's notifications together.
Notification channels let users control your app's notification categories. Android O also adds new visuals and grouping to notifications that make it easier for users to see what's going on when they have an incoming message or are glancing at the notification shade.
PIP for handsets and new windowing features:
Picture in Picture (PIP) display is now available on phones and tablets, so users can continue watching a video while they're answering a chat or hailing a car. Apps can put themselves in PiP mode from the resumed or a pausing state where the system supports it - and you can specify the aspect ratio and a set of custom interactions (such as play/pause). Other new windowing features include a new app overlay window for apps to use instead of system alert window, and multi-display support for launching an activity on a remote display.
Font resources in XML:
Previously you have to root your Android phone to be able to use fonts, but now Fonts are now a fully supported resource type in Android O. Apps can now use fonts in XML layouts as well as define font families in XML — declaring the font style and weight along with the font files.
To help you integrate better with the device UI, you can now create adaptive icons that the system displays in different shapes, based on a mask selected by the device. The system also animates interactions with the icons, and uses them in the launcher, shortcuts, Settings, sharing dialogs, and in the overview screen.
Adaptive icons display in a variety of shapes across different device models.
For the ultimate in audio fidelity, Android O now also supports high-quality Bluetooth audio codecs such as LDAC codec. We're also adding new Wi-Fi features as well, like Wi-Fi Aware , previously known as Neighbor Awareness Networking (NAN). On devices with the appropriate hardware, apps and nearby devices can discover and communicate over Wi-Fi without an Internet access point. We're working with our hardware partners to bring Wi-Fi Aware technology to devices as soon as possible.
With the advent of Google Play apps on Chrome OS and other large form factors, we're seeing a resurgence of keyboard navigation use within these apps. In Android O we focused on building a more reliable, predictable model for "arrow" and "tab" navigation that aids both developers and end users.
See more features through this link