I don't think the tools on privacytools.io fit your requirements (maybe globaleaks) but this site is a good start
https://www.privacytools.io/blogs https://www.privacytools.io/private-hosting https://www.privacytools.io/secure-whistleblower
Also some of the privacy messengers here (like Briar) have blogging/forum features similar to Telegram, but you can't access them via a browser, so you would have to get everyone to install those apps:
https://www.privacytools.io/privacy-messaging
But realistically speaking like the others suggested: Tor, I2P, Zeronet, etc..