Areca Backup is an open source software, you can see its project in http://sourceforge.net/projects/areca/.
Areca Backup is a file backup tool written in java. It supports data compression & encryption, incremental backup, file history explorer and many other features. Areca Backup also includes a transaction mechanism which guarantees your backups' integrity. --the description is copied from the link above.
Now, we come and see if this OSS satisfy the 3 Prime Directives.
Prime Directive 1. The system successfully accomplishes a useful task.
Areca Backup does do a good job in its task. It provides a very powerful and facilitative backup function. We can easily create a target of folder(s) and backup it. The archives will be save in the defined location and can be managed within the target. Also, targets can be grouped that makes us easier to manage them. When backup a second time, it will compare the existing files with the backup files, only the changes will be saved into the new archive. In recovering, we can either recover the whole folder or select some of the files to recover, that makes daily backup fast. What is more, we are able to choose in with archive we want to recover from. It is really a very helpful backup software.
Prime Directive 2. An external user can successfully install and use the system.
It installation is very easy, just need to run the install package and click next till finish.
However, the guide for new starter is deficient. There is no any guide of what to do to make the first backup archive, even in help website online. It took me several minutes to find out how to start and what a target means. But after beginning, it is easy to use. By adding a initial guide, the familiar time will be shorten from decades of minutes to couples of minutes.
Prime Directive 3. An external developer can successfully understand and enhance the system.
Though there is a source available in download, unfortunately, I did not find any develop-level documentation. I am able to create a project with the downloaded src, and the code is well organized. But it is difficult to read into it without guiding documentation. So I cannot do anything with the project. Thus, I think this Areca fails Prime Directive 3.
Areca Backup is a useful software. It can help us in daily backup procedure. But as an open source package, it is not friendly to external developers. However, considering its value in future use, the investment will prove its worth. Maybe the package will be more developer friendly with some further information from the project admin.