Is there something like Arq compatible with both OSX and Windows ? Features I'm interested in: - must use S3 or similar, as long as it's private and "unlimited

Is there something like Arq compatible with both OSX and Windows ? Features I'm interested in: - must use S3 or similar, as long as it's private and "unlimited" - must support multiple clients, even though I don't need real time sync - should encrypt on the client without need of a separate sw I've been using Dropbox + CloudFogger so far, but dropbox doesn't scale anymore with the quantity of data I have, mostly due to the number of files (and I don't like depending on two different sw for one task).