Our Square Inch Project entry
We're big fans of Hackaday here, so when they announced their Square Inch Project competition we had to give it a go. Language Spy's entry is pretty simple really, an HF receive upconverter for use with VHF radios, in particular cheap SDRs like the RTL chipset USB TV sticks. So it takes 0 to 30 MHz on the input, and transforms it to 50 to 80 MHz on the output. Thus you can listen to all the HF bands with your SDR.
If when the board comes in and we build a prototype it performs well enough to be considered a product, we'll put it in a kit and have it on sale here. Meanwhile take a look at the project page.