Build me a tiny binary for Windows and Mac to post a file and receive a file

Hello, I'm Smile Song, developer in China. I'm interesting your project very well I'm a Good SQL, C++, c#, Python, .Net, swift, object-c, OpenCV, Math, Java, Algorithm expert. I m quite well experienced in these jobs. Let's go ahead with me I want to service for you continously. Thanks

Hi, there I am very much interested in your project with all of your requirements. I have many experiences in building windows and mac app so far. I am sure I can implement all of your requirements. I can start on your project immediately and let me know if you would like to discuss anything further with me. Thank you and looking forward to hear from you soon. Best.

Hello, I am interested with your project and I can do this project with Java and JavaFx, write me for discuss more details, Thanks.

It's a bit odd this is a hourly job? I'd be honest with you, I hate GUI programming, especially cross platform GUI, but I have a proposal for you: we can write that as a pure(pure as no server side scripting required) web client using HTML5 File API, it'll be cross platform automatically! and users won't need to download anything. Well there will be compromises like you can't select folders, you can still drag drop and do multiple selections though. And all downloads will be handled by the browser, so not able to specify that download location. And another suggestion: you can first upload a hash instead of the whole file, with a hash database, you can save lots of bandwidth.