Label connector plugin is the successor of EasyCustomLabeling.
The purpose of this plugin is to simplify the drawing of label connectors, also known as callouts.
EasyCustom labeling did a copy of the dataset to be labeled into a line memory layer. LabelConnector will only take profit of the symbology power of geometry generators and auxiliary data to avoid the data duplication.
It is a temporary solution for QGIS 3.4 / 3.6 / 3.8. QGIS 3.10 now has the native feature of drawing callouts.