OpenSim

OpenSim is an open-source virtual world. The server-side software was built from scratch based on the SL viewer so interaction and features are very similar. Still in the alpha stage of development it has reached a point of actually being useful. It lacks the closed, serious business model Linden has developed SL into. Multiple grids have been developed and there is the option of setting up a standalone sim. Standalone sims, grids and sims linked to grids can also connect to Hypergrid which is basically the Internet of virtual worlds.

OSGrid is generally the largest and best established of OpenSim grids. There is no TOS or AUP aside from the unwritten rule of "plz do not crash grid kthnx" and no cp due to partyvan, thus allowing vast freedom only dreamed about even in SL's most liberal times. Many other grids are similar and have few limitations on content.

With OpenSim you can use your own server and not have to pay hundreds of jewgolds for a sim that you are only renting. You can also run as many sims as you want, within resources of your server, of course. You may freely choose names and grid locations in most cases and change either one on a whim without filing a support ticket or paying fees.

Being buggy and still only semi-stable crashing sims is not even a challenge and unless someone was actually present may just be written off as a random crash with little drama. Trolling or griefing is certainly possible but not usually worth it. Sim owners have far more power to b& you than on SL. Most grids lack the mass furry population and general fail of SL.