For some prominent writers, joining the newsletter platform Substack has become a declaration of independence from traditional news organizations, or an ambitious attempt to build a new model for publishing.

For Tina Brown, a Brit who became synonymous with Manhattan media in the 1980s and ’90s, it is something less grandiose. It is simply a chance to have fun.

“This is just an extra something I’ll be doing on a Monday afternoon,” she said in an interview last week.

Her newsletter, Fresh Hell, is set to debut on Tuesday. In an introductory note to readers, she said the title referred to the experience of waking “every day to a news alert from Hades.” The newsletter, she said, would be written mostly in weekly “notebook form,” rather than “Big Think columns.”

“Writing in that private voice is what I’m interested in doing now,” Ms. Brown, 70, said in the interview, held in her apartment in the Sutton Place neighborhood of Manhattan.

She hopes the diary approach will also help in “limbering up” her voice for a planned memoir, she said. A subscription will cost $6 per month or $50 per year.