The Fallible Ideas discussion group is currently active (link) and discusses philosophy and its implications, especially the ideas of Elliot Temple, David Deutsch, Karl Popper and Ayn Rand. The discussion group started in 2013 and this archive goes through 2018.
There's a ton of content here. Don't try to read it straight through. Skip parts that don't interest you, skim for parts you like, or search for keywords to find specific topics you want to learn about. This short video tutorial explains the best way to search. Also, text is frequently repeated because people quote what they're replying to. If you remember what a quote says, you don't have to reread it.
Note: The PDF is very large (74,582 pages). It works fine with Adobe Acrobat Reader. Don't try to open it in Preview (very slow), and it may not work well in other apps.
The Beginning of Infinity is a book by David Deutsch. The discussion group studied and analyzed its philosophy and implications from 2011 to 2017.
Note: The PDF is very large (18,493 pages). See the notes above about large documents.
Taking Children Seriously (TCS) is a parenting and educational philosophy invented David Deutsch and contributed to by Elliot Temple. This email discussion archive goes from 2002 through 2015. After that, TCS discussions have taken place at the Fallible Ideas group.
Note: The PDF is very large (25,054 pages). See the notes above about large documents.
Searching a PDF should be instant, but Adobe broke it so that it can take a few minutes. There are two solutions. First, if you leave a PDF open long enough (can take a couple days for a huge file), it will generate an index file to allow fast searches. Second, to avoid waiting, you can download a file below, put it at a location, and then relaunch Acrobat Reader or Acrobat Pro.
On Mac, put indexes at: /Users/[Your home folder]/Library/Caches/Acrobat/DC/Search/[file.idx]
On Windows, put indexes at: C:\Users\[Your home folder]\AppData\LocalLow\Adobe\Acrobat\DC\Search\[file.idx]