Ask HN: Where do I find a custom browser/app?

I hope to find a custom app (perhaps a tiny web browser?) that comes in Windows, Linux and Mac varieties, graphically interprets Javascript and CSS and HTML like a normal web browser, can maintain 4 keep-alive connections with the server by default, and has customizable HTTP header settings.

I would like this special browser/app to be used by the folks who participate in our future live online auctions. This app should be customizable on the server before the bidder downloads it, such that each downloaded copy has a built-in encrypted userID embedded into it which uniquely identifies that particular bidder.

Such a browser/app will need to request data from only one web server, so tabs and location bars and most of the other 'features' common in todays popular browsers are totally unnecessary. The server's URL can even be hard-coded if necessary so the app will have no use anywhere else.

Any links or suggestions for places where I might find such an app -- or the tools to help me create one -- are greatly appreciated, thanks.