The PC-104 form factor is a venerable stackable form factor that comes in several flavors. The original form factor included only an IDE bus for stacking. Newer versions include a PCI bus in addition to the IDE bus, while a version known as PCI-104 removes the IDE bus and includes only the PCI bus.
Embedded Planet's products offer configurable memory options and are supported by Linux Board Support Packages and VxWorks Board Support Packages.