At first only Chase Bliss Audio pedals could interface with the Empress Midibox. You need to flip the tip and ring for it to work.

Then Alexander Pedals got into the ring with Midibox compatibility. By ring I mean, the ring between the tip and the sleeve. Actually, I don't think Alexander Pedals do anything with the ring so forget I said that.

Then Distaster Area started making controllers with a Multi-jack output. This output has the capability to produce the same output as a Midibox.

Then Meris started making pedals that were compatible with the Midibox. All their pedals are compatible.

Bondi Effects is about to release the Art Van Delay which will be Midibox compatible!

Now there's even a bunch of different Midiboxes on the market! Woo hoo! I'll 

Empress Midibox2 : the one that started it all! (well not really, I guess the midibox started it all). Also, the ugliest of all the midiboxes. Has midi return on the ring of output 1, for extra functionality. To use with Chase Bliss you have to do some soldering.

Chase Bliss Audio Midibox : internal jumpers to make it easy to use Chase Bliss or other pedals. No soldering required.

Meris MIDI I/O : Has wireless compatibility with bluetooth MIDI adapter?!? Crazy!

Disaster Area MIDIBox : also has internal jumpers.

Then the MIDI Association said to hell with current loops, let's just set a standard for DIN to TRS. And then went with the same thing that the Midibox uses!

Hopefully we can get some other manufacturers to make their stuff compatible with the Midibox. Please bug them for us :-)