While RISC OS was influential, the 'app bar' idea mostly came from Windows 1.0 with minimized apps at the bottom of the screen. It went through several iterations and for a while it was a storage location for documents with no apps at all. Eventually the simple app list tested best so that's what stuck.

[I worked on parts of the Win95 UI although George Pitt I think did most of the work on the Taskbar itself]