Bitcoin is the king of digital currencies, at least for the time being. There are several competing digital currencies, however, that could one day rival bitcoin.
Many of these currencies claim to offer certain technical advantages over bitcoin. Other currencies are taking a whole new angle on digital currencies, trying not just to offer an alternative to cash, but also to offer software development opportunities, social media platforms, and other services powered by the blockchain.
For now, bitcoin enjoys a huge lead over the competition, at least in terms of market cap.