2-pin Charlieplexing configuration (actually, just a complementary or anti-parallel configuration) with individual resistors to drive two different LEDs with the minimal number of port signals (without using GND). If two identical LEDs are to be used, this can be further reduced to a single resistor. It can also be used in conjunction with a 3-pin dual-color LED in serial configuration. While intended to be used to illustrate the Wikipedia article on Charlieplexing, it may also be used for other purposes, e.g. to illustrate a polarity indicator etc.
Own work
Matthiaspaul