Bacula
Bacula is a pretty complete backup solution, written in C++, based on three main daemons (file, storage, director) allowing to schedule jobs and restore backups from a given point in time.
Bacula agents
The director service is in charge of orchestrating all operations (start a backup, start a restore, …) and would store its indexes into some RDBMS (MySQL, PostgreSQL or SQLite). This is where we would be defining our retention policy and schedule our jobs. Bacula also provides with a Console client – as well as various graphical alternatives – that will connect to your director, allowing you to restore files, check for jobs and processes statuses, logs, …
The storage service is in charge of storing and serving backups. Nowadays mostly used with regular drives, NFS or LUN devices, yet can still be configured working with tapes.
slack-notify
The file service is to be installed on all the servers you intend to backup. Upon director request, it would be in charge of collecting and compressing (if configured to do so) the data you’re backing up, before sending it to your storage service.
Backup jobs may be of type Full (backup everything), Differential (capturing changes since last Full backup) or Incremental (capturing changes since last Full, Differential or Incremental backup), which should allow you to minimize disk space usage.
Assuming you can externalize your older backup volumes to off-line disks from time to time, there is no limit to your retention.
bacula-dashboard
Jobs definition may include running commands prior to or after having run your backup, you may also define commands to be run upon failed backup, … director can be configured to limit how much simultaneous jobs should be running, the last versions of bacula also include bandwidth limitations. All in all, making Bacula a very complete and scalable solution.
Bacula wiki lists several graphical clients supervising your backups. As of right now, I preferred sticking to a read-only dashboard, installed on my director instance, with bacula-web (PHP/gd).