Highpoint technology have been making RAID cards for Macs and PC's under the RocketRAID name for years. They have just released a new range of PCIe cards with 4 USB3 ports and drivers for Mac, Windows and Linux
The new RocketU 1144 cards come in different versions for Mac and PC, with the 1144CM being compatible with Mac OSX 10.6 and above whilst the 1144B is compatible with Windows and Linux.
The card is a PCIe 2.0 card with four USB3 ports but uniquely each port has its own USB3 controller, allowing the full 5Gbps of each port to be used.
This means that by connecting four USB3 drives in a RAID configuration you can access data at up to 20Gbps, twice as fast as Thunderbolt.
Highpoint will be at the National Association of Broadcasters show in Las Vegas, stand SL8826, where they will also be showing a range of Thunderbolt products.
There is more information about the RocketU cards on Highpoint's web site here