csh·il y a 15 ans·discussDropbox + encfs. Works fine for me on all platforms (Windows/OS X/Linux). It has some rough edges though: File update notifications will refer to the encrypted file, and the browser interface will only show you encrypted file names as well.
csh·il y a 15 ans·discussPossible, but inconvenient because the whole volume will get synchronized every time you modify a file.