A lawsuit from Apple has forced HyperMac to stop selling MagSafe-compatible charging cables as of November 2nd, 2010. HyperMac has produced a number of small, portable batteries that can provide power to a variety of Apple portable devices. When connected to a MacBook Pro with their MagSafe-like connector, the "MBP-PRO," the external batteries could be used to charge the computer's internal battery.
The lawsuit claims that HyperMac violated patents related to MagSafe cables as well as other cables that use a 30-pin connection. HyperMac assembled their units using actual Apple parts. Note that HyperMac will continue to sell the batteries, though we don't see how useful they'll be without the cables.
If you're looking to buy one of these, you've got until November 2nd to do so.