Bitcoin Unlimited

Basics

Founded in late 2015
The Bitcoin Unlimited client (wallet) is used to signal support for the activation of the Emergent Consensus protocol which is designed to allow a dynamic block size, by taking advantage of Bitcoin's existing consensus mechanism (commonly called Nakamoto Consensus). Users can indicate a preference on the block size issue, and direct their node to only relay blocks below their preferred size, thus hampering the distribution of larger blocks across the network. This gives a “voice” to all participants of the network and not just miners.
This system allows users to choose the maximum block size they want to accept as valid. However, there is a user-configurable failsafe mechanism that allows users to accept a block larger blocks that are above this limit reach a certain number. This system ensures that no users are accidentally left behind.
In the BU system, node operators and miners can choose their own blocksize limit by modifying their client via a GUI menu. This would, in theory, create a system where Bitcoin scales according to the space needed to accommodate the transactions in the network which is prone to keep growing like Bitcoin’s popularity and user base. As Satoshi Nakamoto once said: “In a few decades when the reward gets too small, the transaction fee will become the main compensation for nodes. I'm sure that in 20 years there will either be very large transaction volume or no volume.”
Bitcoin Unlimited will be activated when the majority of the miners choose to accept and mine larger blocks. The fact that a simple majority of miners can dictate the longest chain (and that the longest chain "wins") is the fundamental truth of Bitcoin's "Nakamoto Consensus" mechanism. Bitcoin Unlimited recognises this. Although it is said that Segregated Witness (SW) activates at a 95% vote, this activation level is simply a convention. The truth is that if 51% of the miners wanted a change, they could simply mine only the changed blocks, and reject all unchanged blocks. Since 51% is the majority of the miners, the changed chain would be the longest, and therefore the "winner". Even more problematic, a majority vote does not guarantee activation. Miners could be lying in their vote, and refuse to activate the change when the time comes, or revert it after a few blocks. This strategy, incidentally is devastating for Segregated Witness since it would allow the miners to steal all the coins that have been spent as SW transactions. So these higher layer activation protocols fundamentally rely on the honesty of majority of the participants.
"Viabtc is famed as a major supporter of bigger blocks and in 2016 mined the first Bitcoin Unlimited block. It also proposed the name for Bitcoin Cash."

Team, etc.

Rizen, Peter R
Stone, Andrew; lead developer
Suisani, Andrea, early developer
Trevin Hoffmann
Tschipper, Peter, early developer
Clifford, Andrew
Zander, Tom; developer
Harding, Tom; developer
Antony Zegers, otherwise known as Mengarian, decided that he would no longer like to be a member of the Bitcoin Unlimited (BU) development team. According to Zegers, BU as an organization “is too closely associated with the Bitcoin SV community.” Following Zegers’ departure, Amaury Séchet, the Bitcoin ABC lead developer, also decided to renounce his BU membership. Independent member Tomislav Dugandzic also renounced his membership a day later.
Justin Bons; voting member