pouët.net

ZX-81 machine has has 1Kb or RAM (with possibility of extention to 16Kb or more), no sound (well, in specification You will find such an info), only black/white colours and resolution 32*24. The comp is simply a CPU with some RAM on the mainboard, nothing more.

This is (one of the best) ZX-81 arcade-game, made for ZX-81 16Kb (the most standard config) in 1986 by Tadeu Curinga.
Type LOAD "EBDT-INF" and press ENTER.
Emulator: http://www.chuntey.com/
The game ISN'T EASY but it's really cool (not for nervous people 'though ;) ).
Controls: arrow keys (5-left, 8-right, 0-jump, 6-down: from a rope).

A Pitfall look-a-like on the ZX81 .. *daumenhoch*

Somehow I doubt that this really is a scenerelease...

indeed:

"Treasure Hunter ("Em Busca dos Tesouros", "Searching for Treasures" or "In Search of the Treasures" in a literal translation) is a game developed in Brazil, released in 1986 for the Sinclair ZX-81 and its Brazilian clones (TK-82C, TK-83, TK-85 and CP-200S). Inspired by the success of David Crane’s Pitfall, developed for Activision in 1982 and released for the Atari 2600 and other classic videogame consoles and microcomputers, EBdT was written in two years by then teenager Tadeu Curinga da Silva and sold by mail (in either cassette tape format or as printed assembly source code ready to be typed) by the first Brazilian microcomputer magazine, Micro Sistemas."

so it was originally a commercial game. this page has some more info...

Yes but I think it could be here now because of this
"After disappearing for 15 years, a cassette tape with the game was recovered by classic computer collector Kelly A. Murta. The game’s author, Tadeu Curinga da Silva, was located in 2006, and kindly allowed the game to be distributed through the Internet."
Well, whatever. It's a cool game anyway.