Rock Soapwort.  This is a lovely and tough rock garden or crevice plant from the Pyrenees where it grows in exposed sheer rock faces.  Dense cushions of close-packed rosettes with narrow short green leaves.  Pink-purple flowers are held on short 2" stems in groups of one to three.  One becomes a group when hanging with the Threes.  Full sun, good drainage, zones 3-8.