These notes contain speculations about interesting situations that might occur when two or more low-energy positrons interact with each other and/or with various forms of ordinary matter. Topics include many positrons compressed to high density at a field emission tip, a long-lived metastable cold neutral electron positron plasma in a box, dipositronium and other multipositron molecules, the positronium Bose-Einstein condensate, precision measurements on positronium cooled by a pulsed laser method, stimulated emission of annihilation radiation, head-on collisions of two positronium annihilation gamma-ray laser pulses, and possible uses for gamma-ray lasers.