K8IQY MagicBox, a T/R controller that lets you connect a QRP transmitter, receiver, antenna, and key and gives back full- or semi-QSK, RX muting, and sidetone. It provides an easy way to interface all sorts of little transmitter and receiver projects so that they can be easily used on the air. The Four State website goes into greater detail.
I got my kit from someone on QRP-L who decided not to build it, and found that the kit was well documented and went together easily and quickly. I tested it and made a QSO using a Tuna Tin 2 I'd built up Manhattan style. The board is designed such that no enclosure is needed and uses PCB-mount jacks for all connections, so it was easy to try without an enclosure. Which was great, because for a lot of us, finishing the project by mounting in an enclosure is the hardest part. It certainly is for me, and I had a bare MagicBox for months.
I left it at work, thinking I'd be able to get one of our shop guys to help me with it, but that never happened. I finally conned NA4SO into helping me drill the holes, but we did run into a problem with the drilling template. It was a little off, although I thought I'd confirmed it was OK (measure twice, cut once!). Not too bad though, and the easiest solution was to pull the BNC jacks off the board and use panel-mount jacks.
I set mine up with a power LED, a semi/full QSK switch, spot switch, and tune pushbutton. The only problem with any of this was with the spot switch - the early kits were supplied with a "bleed-through" resistor that was too large a value - I paralleled a 100 Ohm trimpot with this resistor and now the spot function works as it should...with the added benefit of being adjustable...this could even be routed to a pot for front-panel control if desired.
Right now, I'm using my old Drake R4 for an RX, but eventually hope to build something up from scratch. All-in-all, I think it's a great kit and well worth looking at if you need to interface QRP "seperates".