The asymptotic necksizes of a fournoid must satisfy the spherical fourgon inequalities. This applet demonstrates the subset of the moduli of fournoids which satisfy two further conditions: the sum of the necksizes is at most 1 (the round cylinder has necksize 1/2), and at least one pair of opposite ends has equal necksizes.
Java NoidViewer archive: NoidViewer.jar
FournoidViewer image library: FournoidImage100.jar
Java NoidViewer source code: NoidViewerSrc.jar
NoidViewer uses the following JavaView archives: javaview.jar jvx.jar