If you want to register with other grids, you really ought to be looking at their web sites rather than this one ;-)
You will need to find the Login URI (including port number) of the grid that you want to log into, with whom you will have registered previously via their web site. Our instructions on connecting will otherwise be the same for these grids. The most common ports are 8002 and 9000 but many grids use custom ports instead, including the default port 80 (i.e. unspecified).
TheHyperGates.com, OpenSimWorld and Hyperica may also be useful for details of Login URIs, which are also used for Hypergrid teleports. This lets you visit grids without registering with them, starting from another grid with which you are already registered. Please see our brief, helpful instructions on how to use Hypergrid to teleport to and from other grids.