Here is my list of solo developer blogs. Usually they are on topic. This does not include personal blogs I follow that happen to be developers.

@mdo (Bootstrop) - http://markdotto.com/

Keith Cirkel - https://www.keithcirkel.co.uk/

Coding – Corbin's Treehouse - https://www.corbinstreehouse.com/blog

Aaditya Purani – Ethical Hacker - https://aadityapurani.com/

Ben Balter - http://ben.balter.com/

fulldecent - https://privacylog.blogspot.com

Orange - http://blog.orange.tw/

Cocoa with Love - http://www.cocoawithlove.com/

Mark Otto - http://markdotto.com/

Moxie Marlinspike's Blog - http://www.thoughtcrime.org/blog/

hueniverse - http://hueniverse.com/