Lots of confusion in the replies so let me clarify:
nostr:nprofile1qy88wumn8ghj7mn0wvhxcmmv9uq3wamnwvaz7tmjv4kxz7fwwpexjmtpdshxuet59uqzqawhxlp5wfr3q2wyfpmtxvxj9ppg3fp80x6erghdfk4pcmq8a7hhwp9puf is an app that uses MDK to be a Marmot compatible client. White Noise isn't going anywhere, we continue to build it out as fast as we can.
MDK is a software developer kit: A library that developers who want to implement interoperable secure messaging will use to create their own apps (like White Noise or for other use cases).
Marmot is a protocol: A plain english description of HOW to implement secure messaging using MLS and Nostr. The protocol spec isn't code, it's just words describing in painful detail how it all works.