What is the best mouse and keyboard sharing software?

If you use 2 mice and 2 keyboards simultaneously, there are issues with keyboard focus. For the first PC keyboard to work on the second computer, you need either to use hotkeys to switch focus, or to use the first PC mouse to move the cursor to the second computer. If the cursor is moved by the second PC mouse, the first PC keyboard focus will not switch, causing a confusion, when one keyboard works on both computers, but the other keyboard works on one computer only.