For Linux

SqlBak for Linux
is free for up to 5 servers

Send backups to:

Local/Network folder, External HDD/NAS
FTP
Amazon S3
Dropbox
Google Drive
OneDrive
OneDrive for Business
Windows Azure Storage
Linux
Free
up to 5 servers
Server down alerts every 5 min
Backup History 12 months
AES Encryption
Server health check every 60 min
Extended support
Need more than 5 servers?