With this app, any device can get the heads-up notifications introduced in the new Android 5.0 "Lollipop", no root required. But according to Addictivetips, this app is much more than just a backport. And according to the users, this app is way better than the original!
HIGHLIGHTS:
Displays the latest notification as a floating popup, complete with full text and quick actions (4.1+).
Works on everything running Android 3.1 and newer.
You're in charge: five pages of customization means you'll get notified your way.
Pocket detection / active display - when you get a text, it'll turn the screen on if you take your phone out of your pocket! (Kinda like AcDisplay. Note: this causes a tiny increase in battery usage if you get a ton of notifications)
Privacy on the lock screen (and in general - this app doesn't even have internet permission, so it can't send your private data anywhere)
Oh, and it's known to work on rooted smartwatches.
LANGUAGES:
Heads-up notifications is available in 20 languages:
English
Arabic (99%)
Bulgarian (71%)
Chinese Simplified (90%)
Chinese Traditional (72%)
German (72%)
Greek (71%)
Indonesian (99%)
Italian (99%)
Norwegian Bokmal (99%)
Polish (99%)
Portuguese (87%)
Russian (99%)
Serbian (Cyrillic) (91%)
Slovak (99%)
Spanish (74%)
Swedish (72%)
Ukrainian (99%)
French (100%)
Turkish (100%)
If you want to help translate, head to https://crowdin.com/project/heads-up . Email me if you need help translating
COMMON ISSUES:
If no popups appear, please make sure that Heads-up shows up in the list of running services. If it doesn't, make sure you have enabled the service, and then reboot the phone.
If your device is running Android 4.2 or earlier, and you have other accessibility services running (such as Pushbullet), they might block Heads-up from receiving your notifications. Please try to disable them if Heads-up doesn't work.
Huawei, XIAOMI and MIUI users: please allow Heads-up to display popups under Settings > Apps > Downloaded > Heads-up. It might also be necessary to reset the app data/settings.
Uninstalling: If you find that the uninstall button is disabled, go to System Settings > Security > Device administrators > Heads-up, and tap Disable.
Other: Facebook Messenger, AcDisplay and PushBullet notification mirroring conflicts with Heads-up. And no, it doesn't display more than the latest notification (after all, this is meant for instant notifications when using the device, not as a lock screen).
OPEN-SOURCE:
Heads-up is now open-source!
If you want to help out, jump in at:
https://github.com/SimenCodes/heads-up/
If you experience any issues, or have feature requests, please open an issue at:
https://github.com/SimenCodes/heads-up/issues/
If the app crashes, please tap 'Report', then 'Send'. This makes it far easier to find and fix the issue.