So I have just posted the paper outlining the proof-of-work problem for my upcoming cryptocurrency Nebula. Here is the link for the paper. I hope to launch Nebula as soon as possible.
The idea behind Nebula is to use a reversible computing optimized proof-of-work (RCO-POW) problem instead of an ordinary proof-of-work problem (if you do not know what I am talking about, I suggest for you to read the original paper on Bitcoin). An RCO-POW problem is like an ordinary proof-of-work problem except for the fact that the RCO-POW problem can be solved by a reversible computing device just as easily as it can be solved using a conventional computing device.
It is very rare for a problem to be solvable by a reversible computing device using just as many steps as it is solvable using a conventional computing device. In general, it takes more steps to solve a problem using a reversible computation than it takes to solve the same problem using conventional computation. Therefore, since reversible computation has this computational overhead and since reversible computers currently do not exist, chip manufacturers do not have much of an incentive to manufacture reversible computing devices. However, since RCO-POW problems are just as easily solved using nearly reversible computational devices, chip manufacturers will be motivated to produce energy efficient reversible devices to solve these RCO-POW problems. After chip manufacturers know how to produce reversible devices that can solve these RCO-POW problems better than conventional devices, these manufacturers can use their knowledge and technology to start producing reversible devices for other purposes. Since reversible computation is theoretically much more efficient than conventional computation, these reversible computing devices will eventually perform much better than conventional computing devices. Hopefully these reversible computational devices will also eventually spur the development of quantum computers (one can think of reversible computation as simply quantum computation where the bits are not in a superposition of each other).
Nebula shall use the RCO-POW which I shall call R5. R5 is a POW that consists of five different algorithms which range from computing reversible cellular automata to computing random reversible circuits. I use the multi-algorithm approach in order to ensure decentralization and to incentivize the production of several different kinds of reversible devices instead of just one kind of device.
The only thing that will be different between Nebula and one of the existing cryptocurrencies is the POW problem since I did not want to add features which have not been tested out on existing cryptocurrencies already.