BubbleGEM
What is BubbleGEM?
BubbleGEM is a small, resident application originally conceived by Thomas Much. It implements "bubble help": Short hints that are displayed when hovering over a button or another UI element and pressing the right mouse button. It only works for programs supporting it though - which a lot of applications released in the late 90's/early 2000's did. In addition top the original, there are alternatives to BubbleGEM that are compatible with every app supporting bubble help.