Alt coins or Alt currencies

‘Alt’ coins are considered any cryptocurrency or digital token that is not bitcoin (Alt is short for alternative).  Alt coins were a natural progression from the original bitcoin due to the open source nature of the bitcoin project.  Furthermore bitcoin solved a significant amount of problems around the implementation of a digital currency, such as the double-spend problem.  

The theory behind bitcoin was as important as the cryptographic technology in driving others to create their own unique version of cryptocurrency.  Initially others sought to create their own ‘currency’, however it was not long before individuals or groups began experimenting with cryptocurrency and blockchain to solve other real world problems.  

An example is Ethereum, which introduced enhanced smart contracts (bitcoin actually has this ability also, although it is not widely known) and the ability for users to create ‘Dapps’; which are decentralised applications.