Apache OpenOffice

Collabora Online (They also offer Collabora Office that runs on your device offline.)

Cryptee

CryptPad

Etherpad

LibreOffice

Mailfence Documents

OnlyOffice

Proton Docs (an end-to-end encrypted, collaborative document editor found in Proton Drive powered by Proton who also have SimpleLogin, Proton Authenticator, Protonmail, Protonmail Bridge, ProtonVPN, Proton Pass, a “privacy-first” AI called Lumo, and Proton Calendar.)

Rocket Tech Docs (Christian, conservative company)

Rocket Tech Spreadsheets (Christian, conservative company)

Zoho Docs