Studying the threshold of black hole formation via numerical evolution has
led to the discovery of fascinating nonlinear phenomena. Power-law mass
scaling, aspects of universality, and self-similarity have now been found for a
large variety of models. However, questions remain. Here I briefly review
critical phenomena, discuss some recent results, and describe a model which
demonstrates similar phenomena without gravity.Comment: 13 pages, 6 figures; Submission for the proceedings of ICGC 2000 in
the journal Preman