SDS-4 (Small Demonstration Satellite 4) is a small satellite (50 cm cube with mass of 50 kg) developed by JAXA and to be launched as a secondary payload on the Shizuku mission  in mid-2012.
There are four rather specialised systems on the satellite:
SPAISE (SPace-based Automatic Identification SystEm) - test on-orbit a receiver for picking up signals from Automatic Identification System transmitters on ships well out to sea, and determine how space-based reception is affected by interference between nearby transmitters and by environmental conditions.
FOX (Flat heat-pipe on-orbit experiment) - to test whether flat heat pipes work in space in accordance with theoretical models and with tests on Earth
IST (In-flight experiment of Solar absorption rate with THERME) - to acquire information about the effect of sunlight in space on thermal coatings, re-flying the THERME instrument developed by CNES for testing different thermal coatings 
QCM (Quartz Crystal Microbalance) - to test whether a Japanese-manufactured quartz microbalance works well in monitoring contamination of the satellite from assembly to on-orbit operation.
Payloads are separated by bullets ( · ), launches by pipes ( | ). Manned flights are indicated in bold text. Uncatalogued launch failures are listed in italics. Payloads deployed from other spacecraft are denoted in (brackets).