Wordpress is an obvious choice. Can be achieved with plugins. Supports already Activitypub.
Already has the media hosting plugin by nostr:npub1n0sturny6w9zn2wwexju3m6asu7zh7jnv2jt2kx6tlmfhs7thq0qnflahe.
Tumblr being winded down by Automattic might give an opening for people looking for alts.
Substack parallel posting / exporting could allow new people to test nostr.
https://developers.notion.com/ is popular.
What about OpenOffice / Google Docs etc?
Zapier & IFTTT integrations would open a new range of reach.