Qt 5.5 was a major update to the Qt5 tool-kit released in 2015.

Qt 5.5 Linux & Open-Source News

KDE Neon Releases User Edition Tech Preview, Based On Ubuntu 16.04 LTS   KDE   2016-04-20
KDE Frameworks 5.16 Released   KDE   2015-11-14
Various Ubuntu 16.04 LTS Decisions From This Week's Summit   Ubuntu   2015-11-05
OpenSUSE Tumbleweed Lands Many KDE-Related Updates   SUSE   2015-10-28
Qt 5.5.1 Brings Nearly 1,000 Changes   Qt   2015-10-15
Qt 5.5 Officially Released   Qt   2015-07-01
Qt 5.5 Release Date Updated One Last Time   Qt   2015-06-23
Qt 5.5 Release Candidate Finally Appears   Qt   2015-06-22
Qt Is Looking At Making Qt 5.6 A Long-Term Support Release   Qt   2015-06-18
Cross-Platform HiDPI Support Ready For Testing In Qt   Qt   2015-06-04
Qt 5.4.2 Officially Released   Qt   2015-06-02
Qt 5.5 Beta Finally Released   Qt   2015-05-15
Qt 5.5 Now Plans To Ship At The End Of June   Qt   2015-05-13
Many Ubuntu Phone Updates Are Coming Up Soon   Ubuntu   2015-05-05
Qt 5.5 Beta Is Coming Soon, Snapshot Released   Qt   2015-05-05
Qt 5.5 Beta Is Closer With Today's Snapshot   Qt   2015-04-16
KDE Frameworks 5.9 Adds ModemManagerQt   KDE   2015-04-11
Qt Creator 3.4 Is Near   Qt   2015-04-01
Qt 5.5 Alpha Finally Released   Qt   2015-03-17
Qt 5.5 Alpha Is Getting Close, But Still Behind Schedule   Qt   2015-03-02
Qt 5.5 Features: Many Exciting Improvements   Qt   2015-02-19
KDE Frameworks 5.7 Brings Many Fixes, Supports NetworkManager 1.0, Etc   KDE   2015-02-15
Qt3D Will Likely Only Be A Tech Preview In Qt 5.5   Qt   2015-02-09
KDAB Continues Its Overview Of Qt3D 2.0, Demos Custom Rendering Effects   Qt   2015-01-20
Qt 5.5 Is Packing On New Features, Going Into Feature Freeze Soon   Qt   2015-01-13
Qt HiDPI Support Is On Hold For A Few Months   Qt   2014-07-02
Qt 5.3+ To Have Printing Support Improvements   Qt   2014-01-07