I suspect that most of us in the forum aren't entirely sure
what you mean by "able to search and link across projects." Who is
searching, and at what stage, who is linking, and at what stage,
etc.? (You the author, or the users?)
Actually, many of us use FAR (Find & Replace), Zenu (link
checker), and ExamDiff (Compare directories & files) to assist
our help authoring efforts. No product can do everything...
Can you provide some clarity on just what you're looking to
do, asap?
There's not much sense giving you suggestions if
we're not talking the same language.
Good luck,
Leon