Would be curious regarding features and performance comparisons with musl, which seems to come up a little short compared to say gnu libc.
Cosmopolitan Libc is 2x faster than Musl Libc for many CLI programs like GNU Make and GCC because it has vectorized string libraries like strlen(). Musl won't merge support it on x86. I even mailed Rich patches for it years ago.
Cosmopolitan's malloc() function is very fast. If you link pthread_create() then it'll create a dlmalloc arena for each core dispatched by sched_getcpu(). If you don't use threads then it'll use a single dlmalloc arena without any locking or rdtscp overhead.
Cosmo has pretty good thread support in general, plus little known synchronization primitives from Mike Burrows. You can do things like build a number crunching program with OpenMP and it'll actually run on MacOS and Windows.
Cosmopolitan plays an important role in helping to enable the fastest AI software on CPUs. For example, Mozilla started an open source project called LLaMAfile a few months ago, which runs LLMs locally. It's based off the famous llama.cpp codebase. The main thing Mozilla did differently was they adopted Cosmopolitan Libc as its C library, which made it easy for us to obtain a 4x performance advantage. https://justine.lol/matmul/ I'm actually giving a talk about it this week in San Francisco.
Wish there was something like musl.cc, i.e., static GCC less than 250 MiB, for cosmo libc.