Bitcoin XT
  
Bitcoin XT was one of the multiple proposals for fixing the Bitcoin-popularity-problem.
As Bitcoin became more mainstream, transaction times took fo-evaaaaaa. Annoying, especially as more people joined. The Bitcoin XT proposal aimed to solve this issue by increasing the block size from one megabyte to eight megabytes, which would increase transaction speeds eight times. Then, each year after, block sizes would double, which was considered supes aggressive, but also like...a cool way to actually tackle the problem.
While Bitcoin XT started, it was overshadowed by other proposals solving the same problem, like Bitcoin Classic and Bitcoin Unlimited. It’s a tough world out there in the blockchain.