A large organization like Alibaba spending the effort to get Android running on their own RISC-V platform seems like a clear sign that we're on the cusp of seeing RISC-V development and adoption snowball in the next few years.

Could someone elaborate a bit on how RISC-V relates to ARM?

From what I understand the former is a completely open source spec, and ARM is a proprietary one. But both are just specs, right? It’s not as if I can buy a RISC-V CPU from an organization behind it, it’ll have to be from a manufacturer that produces their own RISC CPUs?

Is it also an entirely different instruction set? How does it compare to x86 and ARM in terms of performance?

Last but not least, other than it being free / opensource, what are some of the reasons why anyone would choose RISC? Phrased differently, if they are going to take marketshare in the CPU world in the next decade, what will be the reason?

There are also non-free RISC-V cores, but they essentially have to continuously make the argument for their existence against the free cores that are available (support, verification resources, just being better designs in the short term, already being hardened for proprietary process nodes, etc.)