git annex is an open source project that lets you distribute files around various media (including external HDs, Amazon S3, SSH-connected computers, etc.). It has an fsck command for checking that your data still matches its checksums.

There's a GUI interface that makes it a lot like Dropbox, where you just add files to a folder, and they are sync'd.

It works on OS X and Linux, with an alpha for Windows.

One of the alternative theories is that people form associations between words and referents in a "hard-AI" sort of way, by hypothesis testing. Like, I start out with random hypotheses about which words refer to which objects, and every time i encounter data, I evaluate it for consistency with my hypotheses, and make or break them as necessary.