Chasm is a paid commercial game, not freeware. The safest and most reliable way to play is through official storefronts:
Websites like SteamUnlocked, Repacklab, and others that list "free" versions of paid games are associated with several hazards: Chasm Free Download
A free demo is available on Steam for those who want to try the game before buying. Chasm is a paid commercial game, not freeware