Small yet magical but not unheard of
Remembrall is a tennis ball-sized glass ball. It contains smoke which turns red when its owner has forgotten something and turns clear when remembered.
I claim the event that showed great nerve
It was the object that Harry Potter into his career as Seeker. Harry's catch of the remembrall convinced Professor McGonagall that he had nerve and had a natural talent for flying.
Though I ain't rare there haven't been many
A remembrall is not a rare object in the magical world. But during the entire series, only Neville was the sole owner mentioned.
To the end there wasn't any trace of me
As the series went further the remembrall was barely mentioned. It was mentioned when Neville asked Harry to guess what he had gotten for his birthday to which Harry replied that maybe it was a remembrall. Other than that, there hasn't been any other mentions.
Answer : Remembrall