I just found one, but curious if other members regularly check out other online forums or blogs?

https://productivityguild.com/

I havn't known any other forum than the app-specific forums like Devonthink, Tinderbox and the like.

Nice forum you posted: I like the description on the Agile system they described: https://productivityguild.com/t/agile-results-a-flexible-productivity-system-layer/2858

Very good. Thanks

A lot of the Productivity Guild postings are behind a rather expensive paywall.

A site, related to the Mac Power Users podcast, is

https://talk.macpowerusers.com

There's a broad range of users and a lot of discussion of interesting software

A cousin of Mac Power Users is the Automators podcast, and it too has a forum

https://talk.automators.fm/latest

This thread alone has caused multiple weekends lost to CRIMPing all around the world.

https://talk.macpowerusers.com/t/whats-your-favorite-app-that-even-apple-power-users-dont-know-about-but-should/5233

These are great. Thanks!