Online Backup with Arq and Amazon S3
Backups are something that every computer user is supposed to do but nobody really enjoys doing it. Apple's Time Machine makes it a lot easier, at least when you have a second hard disk or a Time Capsule. However, if you're like me and you don't want to clutter your desk with yet another piece of hardware you might like Haystack Software's Arq popup: true.
Arq works very much like Time Machine but saves your files into your own Amazon S3 account. S3 is not another obscure web service that could go out of business at any time but a professional online file storage service by Amazon (yes, the Amazon that also delivers books to your home). It was created mainly for web developers but is also immensely useful for personal use.
With S3 you pay only what you're actually using. The very reasonable storage prices for S3 have just recently dropped to US $0.03 per gigabyte and month, and the "Glacier" option reduces the costs even more down to US $0.01 if you can wait for up to six hours should you ever need to restore your file.
Arq maintains its own file structure so that it can quickly upload only the files that have changed but you can, of course, also store files manually on S3, e.g. using Panic's Transmit popup: true or simply the Amazon AWS website popup: true.
Addendum: Arq 4 also works with SFTP, GreenQloud, DreamHost, and Google Cloud Storage.