While there is the KDE Frameworks that offers a wonderful set of complementary extensions/add-ons to the Qt5 tool-kit, for those looking for more Qt5 extensions, The Qt Company has launched "The Qt Marketplace" as a source for both free and paid extensions.

Qt Marketplace offers extensions to add additional functionality around the tool-kit, new Qt Creator Plugins, tools, modules, and more. There are 100+ extensions at launch including Felgo that offers additional Qt APIs, Incredibuild as a network-based build system for Qt Creator, Froglogic to help with testing Qt programs, KDAB's KUESA workflow software, and various KDE add-ons.

Developers can either off their extensions for free or at a given price, in which case The Qt Company will take a 25% cut over the first year or 30% cut in subsequent years. The Qt Marketplace allows purchases to either be made a single-time or recurring subscriptions.

More details on The Qt Marketplace via the Qt blog. The marketplace itself is at marketplace.qt.io.