Back in mid-2006, a small article detailing Sierra Online's Growth Drivers was published on Kotaku. It listed several online PC games that were meant to be released by Sierra. Most of them were cancelled, including what would have been both Crash's first PC game and also his first foray into the world of online gaming. The game was set for a release in 2007, but a small copy of its logo is the only thing that's ever surfaced besides some minor details.
This quietly-cancelled game was probably going to be exclusive to China (Sierra Online was focusing there at the time, due to the popularity of casual online games in the country), and it was going to be a "mid-session" title. If you have no idea what that means, don't blame yourself — this term never caught on, and it was always vague at best. It seems to imply that Crash Online would have required players to pay a fee for each play session.
As for what kind of game Crash Online would have been... who knows? The publisher has always kept quiet about it, so we may never find out.