The grid is now listed on iDreamsNet in addition to having been listed on TheHyperGates.com, OpenSimWorld [new in 2015-16], Hyperica, and previously gridhop.net for some time [now defunct for some years]. It does not seem possible to re-register with gridhop.net at present.
N.B. Sadly iDreamsNet was deleted at some time during 2014 and no longer exists. The original hypergrid listing site, gridhop.net, is also defunct. At the time of editing (noted in 2015-12-29, still unresolved on 2016-02-07) it appears that TheHyperGates.com is having some problems with its database although I am assured that the service will be functional following a database sync operation.