Cloud File Storage
Store and share files in the cloud.
Syncing a folder forever and sending one large file once are unrelated problems. For the first, the real fork is end-to-end encryption — Tresorit, Sync.com, Filen and Proton Drive lock the provider out, which also means a lost password loses the files. For the second, WeTransfer, Smash, Filemail and SwissTransfer need no account at either end.
Editor's pick
Wormhole for a one-off send: the link expires on its own, so nothing lingers on a server you forgot about. Nextcloud only if someone will genuinely maintain it.