The Tribute stone is a part of the Tribute to Guthix, now that it has hit 100,000 essence, it can be used as a prayer altar, or, as a small summoning obelisk. It is located north of Falador near the druids Memstix and Rutax. The essence could be pure essence or rune essence but each player can only place one essence in total.
Trivia
Even though only 100,000 essence was needed, you can still place essence onto it, if you haven't already.