The tool shop is open Monday through Saturday, form 6AM to 6PM. Bill runs the shop but his brother Will helps him create inventions. Will usually hangs out in the Town Square but every so often Bill will be in the square AND in his shop. Bill and will are twins so they look exactly alike except for their hair. Bill has pink hair while his brother has bright green hair.
Bill sells tools and machines you'll use on your farm. He sells tools for use on your crops and tools to use on your animals. Once you buy a tool from Bill he wont resale it again, so late in the game after you've bought everything Bill wont have anything for sale at all. Bill also sells the mini games once you have found them.
The twins will also upgrade your Sickle and your Hoe. To upgrade your Hoe, use it until it breaks, then go talk to Bill. He'll take your Hoe to repair it. Return in 3 days to obtain the Super Hoe. To upgrade your Sickle, become friends with Bill and Will and you may eventually receive the Great Whetstone event. If neither of these events happen you can also wait until your birthday and hopefully Bill will come by and offer to upgrade either your Hoe or Sickle as a gift.
After you have 4 cows in your barn, Bill and Will might make you the Cheese and Butter Machines. The machines both take milk (large or small) and convert it into cheese or butter, which you can then ship for more money. Cheese and Butter both sell for 300G each so if you're short on funds when the machines are available you only need to buy one of them in order to earn higher profits.
Once you have 4 sheep they also might make you the Yarn and Knitwear machines. These two machines act just like the Cheese and Butter Machines - place wool (small or large) into the machines and out comes Yarn or Knitwear. Yarn and Knitwear sell for 300G a piece. Some people never get the chance to buy the machines from Bill while others always get the machines. No true way of obtaining these are known as of yet.