Pretty much none. The very funniest one is Intel's "Proof of Elapsed Time", which might as well be called Proof of Buying An Intel CPU. Rather than have miners

Pretty much none. The very funniest one is Intel's "Proof of Elapsed Time", which might as well be called Proof of Buying An Intel CPU. Rather than have miners compete to produce the next block, a timer running in an environment secured by a DRM mechanism built into your Intel CPU picks if you get to do the next block. The white paper is an extended advertisement for Intel® Software Guard Extensions™ (SGX™). Also, they only have a simulated Proof of Buying An Intel CPU mechanism as yet. https://intelledger.github.io/introduction.html https://intelledger.github.io/introduction.html This doesn’t provide any security against malicious participants; the excuse is that private blockchains need speed over security. You might think that at that point you don’t need a blockchain at all, but you’re hardly going to sell any consultant hours with that sort of thinking.