I feel like I'm saying the same things everyone else has said time and time again but here's my attempt to draw it a little closer to an OS.
BitShares is an operating system for the transfer/control/manipulation of value based objects in a manner that is not subject to corruption or coercion.
The current OS, for value objects, can take days to weeks to process a simple instruction. It relies heavily on manual human effort which leads to very slow speeds, easily corruptible, lost, or manipulated data, and very high maintenance costs. Most operations pass through a central authority that can arbitrarily block and or restrict its use. Use of the system is not available to most people, even in the most developed, technology rich areas.
In contrast, BitShares is available to anyone with access to even the most basic technology. Its use cannot be restricted and operations are not centrally controlled by anyone. Processing instructions is distributed across the globe and relies on almost no human interaction which eliminates most, if not all, cases of corruptible, lost, or abused data. Instructions are processed in seconds rather than days/weeks.
The BitShares OS can be used for any purpose whatsoever and makes no attempt to restrict or deny access to its operations network.