Earlier quoted context omitted.
Bitcoin? I thought there are lots of free stuff for that.
GPU's aren't used for mining Bitcoin. Bitcoin's algorithm is CPU-intensive, and is nearly exclusively done on from-the-Silicon-up purpose-built chips like Avalon and Antminer. GPU's are used for mining other cryptocurrencies like Litecoin and Ethereum. These can be traded for Bitcoin or fiat currencies.
Some other cryptocurrencies have algorithms that are designed to be hard for GPUs and ASICs (cryptonote for instance) but I think it's just postponing the inevitable. If those altcoins become valuable enough I'm sure people will start making micro-optimized dedicated hardware to mine them and eventually it won't make sense to use GPUs for them either.