Android P
Alexander 🇷🇴:
Inline photos and smart replies: remember Reply? Now you have that built into Android. Developers can also add support for showing things like images and stickers in-line as well.
Screenshot editing: you can crop and draw on screenshots you capture. This has been a long time coming.
Volume buttons control media volume by default: Android does a lot of things really well, but audio management probably isn't one of those things. Your hardware volume keys control different things, without much of an indicator until you actually press one. Now by default, it's set to change media volume, as opposed to the ringer (as in Android O and before).
Simultaneous connection of up to 5 Bluetooth audio devices: the limit in 8.1 was two, one for calls and one for media. But with P you can allow up to five devices to be connected at one time. No simultaneous playback, though.
Zoom lens for text selection: like iOS has had since forever, when you select text, on P you can get a nice magnified view of the area above your finger.
Temporary rotation lock: a bit difficult to explain, but when you have rotation locked in portrait, a new icon appears on the nav bar when you turn your phone sideways that will quickly toggle to landscape, and vice-versa.
Alarm quick settings toggle: there's a new Alarm tile/toggle in quick settings. It shows the next alarm, gives you a shortcut to all currently set alarms and allows you to easily set new ones.
App notification tracking: if you get an annoying notification, you can easily track down which app it came from. That should help cut down on notification spam (if you have problems with that).
Wired charging sounds: Google never fails to impress. They've managed to miniaturize the machine that goes ping into the Android P developer preview, triggering it every time you plug your phone into power. Ah, technology.
Chrome-like 'feature flags': you know how Chrome has a bunch of extra options called "flags" for enabling testing features or tweaking things? Now Android has the same thing, called "feature flags." Basically, all the unstable testing stuff with convenient toggles in one spot.
Pulling down the notification tray results in vibration: Pretty simple. When you pull it down, you get a bit of haptic feedback.
Offers to hide frequently dismissed notifications: If you keep dismissing the same notifications over and over, Android P will ask if you'd prefer to just have them be hidden.
General visual changes
Display cutouts are supported (i.e., notches): The ZenFone wasn't a fluke, looks like we can expect more phones in the style of the iPhone X, and Android will have software support for them.
Time is on the left side of the status bar: probably in an effort to accommodate notches, Google has decided to move the status bar clock to the left.
Pixel Launcher is shaded, new mic icon, separate tab for Android for Work apps: Google's constantly making little tweaks to the Pixel launcher. Android P brings a few small visual changes, like a new shaded background and mic icon for the search bar, plus a new app dichotomy in the form of two tabs, separating Android for Work apps from personal ones.
New colors and tweaks in Settings: it's bright, friendly, and colorful, à la old-school TouchWiz. You'll probably dig it.
Ambient Display shows battery percentage, centers notifications: notifications are centered in Ambient Display, and you can finally see battery level without turning on your phone.
Night Light toggle shows active time: don't know when you set Night Light to trigger? Now the toggle/tile in quick settings will say.
Quick settings scrolls vertically: pagination is the devil, so with P all your quick settings toggles and tiles can live on one scrollable page.
Volume slider repositioned to the side of the screen, Bluetooth devices listed: Like the power menu in Oreo, Google has moved the volume sliders to be near the buttons that control them, and Bluetooth device volumes are conveniently acc