QGIS is absolutely one of the biggest open source success stories. Its interesting to see the funding and delivery of new features is largely done in Europe where in the US it is extrmely hard to not use ESRI products.
A couple of packages used by qgis worth calling out - postgis which really grew up with qgis, and pdal which is a relatively new but incredible package for working with point cloud data.
Yes, Europe is going the OSS path. I work at University and almost everyone I know in GIS fields switched to QGIS in the past 5 years. Most government departments are also (trying) to switch, some succeeded already (others are waiting for important people to enter pension, so their replacements are more OSS minded).
A couple of packages used by qgis worth calling out - postgis which really grew up with qgis, and pdal which is a relatively new but incredible package for working with point cloud data.