Have you looked at Cloudian? We use it internally at our company to develop our S3 app. I'm using the Community Edition which is free for up to 10TB of storage. It's got pretty good S3 coverage or at least covers most of the stuff my app uses (I use versioning and multipart uploads so I think my app is advanced). The version-ids and multipart ids etc that it generates are different than those you get from AWS but boto has no complaints so far. It also works with s3fs and other s3 bucket browsers that I have tried.
In my opinion it's a good tool for development against the AWS S3 API and should meet your requirements. You can point your app at your local Cloudian server and then when you are ready for production you can point it back at Amazon. Your mileage may vary... Good luck.
