QGIS FlowMapper (by Cem GULLUOGLU) https://plugins.qgis.org/plugins/FlowMapper/
This plugin generates flow lines between discrete nodes for depicting spatial interaction data (e.g. migration, traffic etc.). Plugin can generate Net/Gross/TwoWay flow lines based and also the flow nodes based on an interaction matrix and a pair of coordinates supplied in plain text (txt) format. All outputs are in shapefile format. Flow and node filtering capabilities are available as well as graduated symbology options. Test dataset and brief documentation is included (see 01_test_data 02_documentation 03_screenshots folders).