Microsoft released Garnet last week. Which is meant to be a drop in replacement with 10x the performance, written entirely in C# (incredibly accessable vs C++).
MIT licence, like most of the rest of their tools/libs/frameworks.
Nice part here is that they dog food it, since it's used at scale. So problems tend to get patched quickly by paid devs, while the FOSS community gets to bake in the features they want.