There are a lot of Tool Companies. The biggest names in Cordless tools
Craftsman Tools ( Owned by a Sears Holding company) and are sold at Sears, K-Mart, and Ace Hardware primarily in the United States.
Ryobi is a brand owned by Techtronic Industries of Hong Kong. They are sold exclusively through Home Depot in the United States. Techtronic is a manufacturer that also makes many other brands of power tools as a private label manufacturer. The Ryobi brand is aimed at higher quality homeowners.
Ridgid is also owned b y Techtronic Industries and is only available through Home Depot in the US. The Ridgid brand is aimed at Professional users.
Stanley Black and Decker Company also owns a couple of other big name brands of power tools.
Dewalt is a premium line of contractor cordless and now hand tools.
Porter Cable was at one time owned by the Stanley group but now appears to be back out on their own developing a new line of tools.