In an era of false "firsts", this may qualify as the true thing: a company using one online world to promote another one of their own. The SL island of Myst Online was created to advertise a game of the same name. As it happens, the history of the two worlds extends back several years. Uru Live was the first attempt to create a multiplayer version of the cherished Myst games; when that world failed, and its citizens needed a new place to call home, Second Life was inundated with emigres. Many sought to recreate something like Uru in SL; from them came an early game called The Mysterious Journey, and Numbukulla, an SL-based adventure game that thrives to this day. One of Myst's original creators, it's worth pointing out, is no stranger to SL, which is perhaps why, when it came time to resurrect Myst in a new form, a portion of the world was brought here. Though financed by the company behind Myst Online, the SL component was created by members of D'Ni, a group of Uru exiles. They are fans given a chance to do their part promoting the world they left behind (now reborn with a slightly different name.) What they've created is ornate, evocative, and lovingly detailed, with hints at puzzles and hidden places to explore. (Ironically, the overall effect is somewhat marred by excessive advertising and web links to the official game, jutting up from the rocks and trees like 3D pop-up ads.)
This link is a direct portal to the island, though it probably won't grant you access until tomorrow, after the official opening. Meantime, more images after the leap.