It is not dead, but also not progressing very fast. I think low adoption rate is their biggest hurdle, and subsequent lack of network effects in the development community. Solid based on a bunch of Linked Data standards which find most traction in small academic circles. Few sexy applications or good libraries to build from.
It's not dead! It's just no longer at MIT (as is also mentioned on the website you linked). Tim founded a startup called inrupt (disclosure: I work there, opinions my own) that aims to stimulate commercial adoption. The links in the sibling comment by rapnie are an excellent place to start.
How does an organisation even stimulate others to adopt Solid? I cannot imagine your daily activities. Can you elaborate, assuming you would be comfortable to do so?
I can't disclose everything (I'm not involved with all the parts of the company), but the most important way in which I contribute to that is by building developer tooling and writing documentation for engineers looking to write apps on Solid.
The Gitter channels are apparently most active.
Web: https://solidproject.org/
Forum: https://forum.solidproject.org/
Gitter channels, etc: https://github.com/solid/information/blob/master/gitter-chat...
Repo: https://github.com/solid/solid