Didn't Terry just die recently?
It sadly seems so, but it has not been confirmed.
What is weird is that his site used to have a donations button - https://archive.fo/ltjBH Then someone changed it to suggest donations to charities in honor of his passing - https://archive.fo/M8Iut And now it's completely removed - https://www.templeos.org/
Someone else said he wasn't in wy though.
This is not true. In fact, it is in some sense an affirmation of the reality that the pieces beneath your high-level software are approachable by mortals and not magic. I used to hack on one just for fun. The difficulty is highly overestimated by some folks here.
There are a lot of topics you could go into very deeply and each of these can turn out to be a huge time sink, and the lack of time is the main reason I stopped. Some of my favorite down-the-rabbit-hole sub-topics were filesystems, synchronization, and message passing for a micro-kernel. Each of these could be someone's full time job but they are approachable.