The low cost, small 3.3cm OLED display is fun to play with. The original one I bought has a built-in ROM for some retarded (Simplified) Chinese characters. The ROM is accessible via SPI and the display itself via I2C. Even though getting the characters from the ROM is doable, there is only a very limited set of available characters and is only in Chinese. Worst of all, the characters are not UTF-8 friendly. In order to be able to show multiple languages and symbols, I decided to write a little iPhone app to do all the heavy lifting multilingual works and transmit the results to the display. I swapped the original one with a simpler one without built-in character ROM, thus only 4 wires are required.
The OLED display was driven by a Spark Core using I2C. The rendering and text editing is all done on the iPhone with a small app. The rendered image is then transferred to the Spark Core for display.