Bitcoin XT

• A fork of the Bitcoin Core reference client.
• Mike Hearn published a Bitcoin Improvement Proposal (BIP 64), which started the basis of his alternative client Bitcoin XT. It was built to more easily link with his crowdfunding project called ‘Lighthouse’. A bitcoin-powered app to create and manage your own crowdfunding campaign on your computer. Bitcoin core developer Mike Hearn showcased the app at the Bitcoin 2014 conference in Amsterdam.
• On June 10, 2014 Mike Hearn published a Bitcoin Improvement Proposal (BIP 64), calling for the addition of "a small P2P protocol extension that performs UTXO lookups given a set of outpoints.”
• On December 27, 2014 Hearn released version 0.10 of the client, with the BIP 64 changes.[4] It was intended to support queries for his Lighthouse crowdfunding platform project.
• On June 22, 2015, Gavin Andresen published BIP 101 calling for an increase in the maximum block size. The changes would activate a fork allowing 8 MB blocks (with doublings every two years) once 75% of a stretch of 1000 mined blocks is achieved after the beginning of 2016.
• On August 6, 2015 Andresen's BIP101 proposal was merged into the XT codebase.
• In mid-2015, the concept achieved significant attention within the bitcoin community. Made partly by Gavin Andresen and Mike Hearn
• To address denial of service attacks, Hearn blocked Tor exit nodes in his Bitcoin XT implementation.

Because the idea of censoring anyone’s connection to the Bitcoin network is tantamount to treason, this did not go over well, and may have sealed the fate of the XT project. It quickly began losing support from the community.

• The proposal did not gain the necessary support to go into effect on the Bitcoin network by early 2016, the earliest possible switchover date.
• Bip 101 was reverted and the 2-MB blocksize bump of Bitcoin Classic was applied instead.
• Bitcoin XT software was attacked by malicious software called Bitkiller