Implementation of the standard is still not complete, but in my opinion breakpoints and stepping work quite well! Support for loading systems with ASDF is near.
Let me know if you like it! Support on Patreon or Liberapay is much appreciated
Can you please share more background information about the project, in particular why you wanted to take on this huge challenge, and why you didn't just start from an existing implementation, and why you chose C as the implementation language? Do you assume that you can still use the same GC with the addition of multi-threading?