What you describes sound a whole lot like the core of distributed/decentralized version control systems (DVCS). The most popular DVCSs are Git and Mercurial (and Bazaar to some degree, though it seems an order of magnitude less widespread).
In fact, I'm doing precisely what you describe for some non-programming projects, with Mercurial (specifically TortoiseHg - the equivalent to TortoiseSVN) and it's working perfectly. Git long had a reputation for inferior Windows support and GUI tools, but I wouldn't be surprised if this has changed. I've never really used Git (wasn't ever dissatisfied with Mercurial, so I only use it for checking out the source of projects that use Git), so I can neither judge its fitness for your usecase nor recomment a frontend.