General
Background jobs (cron) can now run in parallel owncloud/core#24696
Update notifications in client via API - You can now be notified in your desktop client about available updates for core and apps. The notifications are made available via the notifications API. owncloud/core#24444
Multi bucket support for primary objectstore integration owncloud/core#24760
Authentication
Pluggable authentication: plugin system that supports different authentication schemes: owncloud/core#23456
Token-based authentication
Ability to invalidate sessions: owncloud/core#24703
List connected browsers/devices in the personal settings page. Allows the user to disconnect browsers/devices. owncloud/core#24703
Device-specific passwords/tokens, can be generated in the personal page and revoked: owncloud/core#24703
Disable users and automatically revoke their sessions: owncloud/core#23844
Detect disabled LDAP users or password changes and revoke their sessions
Log in with email address: owncloud/core#24389
Config option to enforce token-based login outside the web UI: owncloud/core#24779
Two Factor authentication plugins system: owncloud/core#24559
OCC command added to (temporarily) disable/enable two-factor auth for single users owncloud/core#24559
Note: the current desktop and mobile client versions do not support two-factor yet, this will be added later. It is already possible to generate a device specific password and enter that in the current client versions.
Files app
Ability to toggle displaying hidden files: owncloud/core#2589
Remember sort order: owncloud/core#10788
Permalinks for internal shares: owncloud/core#11732
Visual cue when dragging in files app: owncloud/core#20150
Autoscroll file list when dragging files: owncloud/core#22576
Upload progress estimate: owncloud/core#24605
Federated sharing
Ability to create federated shares with CRUDS permissions: owncloud/core#23918
Resharing a federated share does not create a chain of shares any more but connects the share owner's server to the reshare recipient: owncloud/core#24603
External storage
UTF-8 NFD encoding compatibility support for NFD file names stored directly on external storages (new mount option in external storage admin page): owncloud/core#21365
Direct links to the configuration pages for setting up a GDrive or Dropbox app for use with ownCloud owncloud/core#22214
Some performance and memory usage improvements for GDrive, stream download and chunk upload: owncloud/core#23517 owncloud/core#23323
Performance and memory usage improvements for Dropbox with stream download: owncloud/core#23516
GDrive library update provides exponential backoff which will reduce rate limit errors: owncloud/core#20481
Minor additions
Support for print stylesheets: owncloud/core#16857
Command line based update will now be suggested if the instance is bigger to avoid potential timeouts: owncloud/core#23922
Web updater will be disabled if LDAP or shibboleth are installed owncloud/core#24201
DB/app update process now shows better progress information: owncloud/core#24305
Added occ files:scan --unscanned to only scan folders that haven't yet been explored on external storages owncloud/core#24702
Chunk cache TTL can now be configured: owncloud/core#24812
Added warning for wrongly configured database transactions, helps prevent "database is locked" issues owncloud/core#24889
Use a capped memory cache to reduce memory usage especially in background jobs and the file scanner owncloud/core#24351 owncloud/core#24869 owncloud/core#24405 owncloud/core#24403
Respect CLASS property in calendar events owncloud/core#24080
Allow addressbook export using VCFExportPlugin owncloud/core#23893
Birthdays are also generated based on shared addressbooks owncloud/core#23510
For developers
New DAV endpoint with a new chunking protocol aiming to solve many issues like timeouts (not used by clients yet): owncloud/core#20118
New webdav property for share permissions owncloud/core#22789
Background repair steps can be specified info.xml owncloud/core#24274
Background jobs (cron) can now be declared in info.xml owncloud/core#24392
Apps can now define repair steps to run at install/uninstall time owncloud/core#24322
Export contact images via sabre dav plugin owncloud/core#25081
Sabre DAV's browser plugin is available in debug mode to allow easier development around webdav owncloud/core#23368
Technical debt
PSR-4 autoloading forced for OC\ and OCP\, optional for OCA\ owncloud/core#13241 docs at
https://doc.owncloud.org/server/9.1/developer_manual/app/classloader.html More cleanup of the sharing code (ongoing): owncloud/core#22209