Microsoft has chosen to not release a 64-bit version of Jet, their database driver for Access. Does anyone know of a good alternative?

Here are the specific features that Jet supports that I need:

• Multiple users can connect to database over a network.
• Users can use Windows Explorer to copy the database while it is open without risking corruption. Access currently does this with enough reliability for what my customers need.
• Works well in C++ without requiring .Net.

Alternatives I've considered that I do not think could work (though my understanding could be incorrect):

• SQLite: If multiple users connect to the database over a network, it will become corrupted.
• Firebird: Copying a database that is in use can corrupt the original database.
• SQL Server: Files in use are locked and cannot be copied.
• VistaDB: This appears to be .Net specific.
• Compile in 32-bit and use WOW64: There is another dependency that requires us to compile in 64-bit, even though we don't use any 64-bit functionality.