Eurorack is already pretty small as a format, however 2HP take the concept of small format modular and really go to town with it.
HP is the width of measurement used for the eurorack format and 2hp is really the smallest width you could ever hope to fit anything functional in.
2hp specifically make modules in 2hp.
More info at 2hp
Novel way to demo the super low cost bus powered mini synth
We take a look at the new Novation Polysynth