It is an "universal" table (used for skills, combat, etc.) from the Brazilian RPG Tagmar (supposedly based on Star Frontiers, not FASERIP).
Looks nice, huh?
But in combat, it really shines. You basically compare your opponents defense (and armor, I think) to your attack and check the corresponding column. Weapon damage s fixed, and each color corresponds to a fraction of total damage: 25%, 50%, 75%, 100% and 125%.
Here is another rendition (from another edition, I think):
So, even tough you have to look at a table, you save one roll (you do not roll for damage) and you don't even need math (damage is written in your sheet, something like "Sword +15 damage 3/6/9/12").
A natural 20 (grey) is always a crit and makes you roll again in the same table. Although the average damage is not necessarily that great, rolling 20 again means gruesome death (beheading, impaling, etc., depending on the weapon).
Talk about gritty!
This looks very cool IMO. It would be nice to make a D&D version at some point.
I guess I would fix a few things: some columns are identical, critical from inexperienced fighters shouldn't be so extreme (although the game make "minions" scary on purpose), experienced fighters shouldn't fumble on a natural 1 (although that is optional, I think), maybe three kinds of damage would be enough (33%, 66%, 100%, for example) etc.
But I like the idea of having attack and damage in a single roll, and even having a big, fixed number for combat (say, you deal 32 damage with your axe), but seldom using your weapon's full potential.
It would be a great way of differentiating weapons and making them more unique without being too fiddly.
Of course, this means you'll ALWAYS be consulting a table... It'd better be printed in your character sheet!