Control panel applets
Microsoft has been calling the mini applications usually launched from the Windows control panel 'applets' since there's been a control panel.
I'm sure there are much older references which could be found with a bit of effort, but search for the term has this link at the top of page 2 to a 2002 article referring to control panel applets:
According to the OED the suffix -et (or -ette) is borrowed from french (as many words such a table are) and can mean:
denoting relatively small size
denoting an imitation or substitute
denoting female gender
Now I'm sure that when choosing the prefix 'app' Microsoft had only one idea in mind - that the programs run from the control panel are (app)lications. Not, for example, (app)liances, (app)aling or (app)ealing. Being focused on assisting with the configuration of a small sub-set of the OS it was understandable they would want to convey idea by using the commonly used -et suffix with its implication of the named thing being small.
So the term 'applet' has not only prior art but is the joining of acommon contraction and a common suffix. No judge is going to side with Apple on this one.