https://solotravelerworld.com/
I have subscribed to their newsletter for a while, and there's always a lot of good info for solo travelers. They only accept ads and promote tour companies with a single supplement no more than 20%. And there are a lot of good articles on their website.
Maybe other folks have some other good resources for solo travelers to add to this thread.
And Webmaster, perhaps you'd consider adding a Solo Travel section under Tips and Trip Reports?