For years around geospatial open-source community I have developed dozens of QGIS and GRASS plugins. Many of them were institution-specific, but some are for general purpose, and they are published in QGIS standard repository.
Attribute based clustering is dedicated to problem of objects clustering based on their semantics. Plugins implements hierarchical and K-MEANS algorithms and Elbow method for clusters number optimization. This plugin reached more than 40k downloads.
Minkowski dimension calculator allows to estimate fractal dimension for vector features. Fractal dimension is interesting characteristic of feature geometry, which can be connected with nature and genesis of geographic object.