Like Toribash and Rag Doll Kung Fu, Triachnid is based on ragdoll physics -- that is, the character you control is a jointed model that behaves according to the rules of physics. In Triachnid, you move your three-legged character by picking up its feet in turn with your mouse, and flinging them against a surface -- since your character is bug-like, the feet can adhere to almost any surface, and you can climb sheer cliffs, or even hang upside down.
As with other games that depend on ragdoll physics, there's a bit of a learning curve involved, since the UI is quite different from what we normally expect. Thankfully, your character is three-legged -- managing an arachnid's eight legs would be inordinately tedious.
The game is, in essence, a level-based platformer; the basic rule is that you must get your triachnid across each level, along with its egg case, which you can carry in your mouth. Falling rocks and sharp edges can cause you to lose health and, naturally, if you lose too much, you die. (There are no saved games in Triachnid, unfortunately, so if you want to complete it, expect to spend a fair amount of time mastering the interface.)
Triachnid can also spin webs, which can be used to capture flies to regain health; your spinneret can be used to rappel down, as well. Some levels have larvae you need to rescue, too.
Triachnid's stark graphics, reminiscent of Mars or the southwestern desert, coupled with haunting, minor-key acoustic music help set an emotional context rare in games: a feeling of poignancy, appropriate to a game in which you're striving to rescue an endangered critter in a hostile world. Success leads to quiet satisfaction, rather than fiero.
On the whole, a charming and quite original little Flash game.