Kapner is best known for his activism on the internet. On his website, Real Jew News, which was for a time known as Real Zionist News, he writes articles on topics related to Jews from a critical perspective. As well as his own website he publishes short videos on YouTube which cover the same topics.
There have been various controversies and criticisms. See the "External links" section.
Opinions of Kapner on forums such as Stormfront have varied greatly.