Horsebow (3.5e Equipment)
From D&D Wiki
The Horsebow (also called a cogbow, or boxbow) is a type of crossbow that employs winches, gears, and cogs to significantly increase the possible damage, accuracy, and range of said bow. Loading a horsebow is slightly different from loading other items, as there is a variability that other weapons do not have. If the winch is only winched once, (a full round action) it deals the amount specified above. For each aditional winching, however, an aditional 2d6 is added for a medium sized, 2d4 for small sized, or 2d8 for large sized. The maximum number of winchings is 5 total. This takes 5 rounds.
A critical maximizes all numeric values, then adds an additional 2d4(small), 2d6(medium), or 2d8(large) damage.
Normally, operating a horsebow requires two hands. However, you can shoot, but not load, a horsebow with one hand at a –4 penalty on attack rolls. You can shoot a horsebow with each hand, but you take a penalty on attack rolls as if attacking with two one-handed weapons. This penalty is cumulative with the penalty for one-handed firing.