I started thinking about Arq back in early 2009 because I wanted an easy-to-use backup program but couldn't find one that worked well. I liked Time Machine and even bought a Time Capsule so I wouldn't have to remember to plug in an external hard drive. But it still only backed up when I was at home near the Time Capsule, and if my house burned down or someone stole my computer and Time Capsule my stuff would be gone. I wanted online backup, at least for my most important documents and photos.
I tried Mozy, Carbonite and Backblaze. They all offered "unlimited" size backup for a fixed fee, but the "unlimited" service had limits. I couldn't back up a network drive, for example. I couldn't keep backups of external drives reliably -- Backblaze promised to delete backups of external drives that haven't been connected for 30 days. They were vague about durability and availability of my backups. And then there was the risk of the backup storage provider closing up shop and me losing all my backups. I'd seen that happen before (Upline, Xdrive, Omnidrive, Digital Railroad).
Amazon S3 seemed like a great place for my backup data. It's backed by the power of a large, profitable, public company. It offers clear durability and availability numbers and replication to multiple data centers. And it isn't an "unlimited" type of offering, so they don't add constraints to minimize the amount of backup data I have.
Backing up to S3 felt like real backup, but there wasn't any great software to do it.
I had been working on a project that used Amazon S3 for storage, and stored its stuff as a content-addressable storage (CAS) system, written in Java. I decided to rewrite those bits in Objective-C. Then I added logic to correctly back up all Mac-specific metadata, plus strong encryption, plus a simple but powerful Mac UI. That became Arq.
It turns out lots of people were looking for something similar, and through word of mouth Arq has become very popular among Mac users. Since then we've added a lot more storage options besides Amazon S3, plus a Windows version of Arq!
We believe people should have control over their digital lives, including their backups. We believe people can get the benefits of cloud computing without having to give up privacy or security.