Atari have announced that the next generation of RCT, called Rollercoaster Tycoon World (RTCW) will be released on December 10th. It's available in 3 versions, and can be pre-ordered at http://store.steampo...com/app/282560/ . Initial release will be for PC and Linux, with a Mac version in the works for future release. You can read the official announcement on STEAM http://steamcommunit...499623792383117
People who pre-order will have access to 2 pre-release beta weekends at the end of October and November.
There's a 50+ minute video of the game here. Fast forward to 6 minutes and 5 seconds.
It's possible that the tools for creating User Generated Content (UGC) may be available before the game release. It looks as though (unconfirmed) that only scenery and peeps will be supported initially. Multiplayer will not be part of the first release, but Atari are saying it will come later as a free upgrade.