Other crypto currencies
Bitcoin is not the only game in town. Since the core code is open source, many people have created their own crypto currencies. Some of them, such as litecoin, have developed a substantial following. Others, such as dogecoin, try to remain ironic but are gaining a life of their own that may overwhelm the original humorous intent.
My research was enabled by kind reader gifts of bitcoins several years ago. Would you like me to explore further in the crypto currency universe? Send me some coins to the addresses above to use in the experiments, and I'll report back!