To the current fans and potential future users: the open source RAW developer RawTherapee 4.1 is out. (There is a thread about it here, which focuses on support for medium format cameras in RT: http://www.luminous-landscape.com/forum/index.php?topic=90105.0
One of the new exciting features include the support for high-dynamic-range DNG files. This means that RT can now read DNGs with 32 bit per channel data - essentially the format of HDR images. Then you can use the floating-point-precision tools in RT (curves, etc) to tone-map or otherwise treat the files. Another selling point is that the demosaicing algorithms still can be changed freely, flatfield correction still works, etc.
A caveat: you do not import 2 or more RAW files to create a HDR image or a DNG file in RawTherapee! You have to use a different tool for merging the RAWs into a single HDR DNG file. You can then use RT to open the DNG RAW file as if it has been made as a single exposure.
Detailed info on the HDR DNG support and what it means for e.g. "noiseless" images: http://rawtherapee.com/forum/viewtopic.php?f=1&t=5426
Overview of the 4.1 release: http://rawtherapee.com/blog/rawtherapee-4.1-is-out