The Gamma World 3e RPG released in 1986, and the rules were completely changed from the prior GW iterations.
I’ll quote my own RPG reference site:
Where 1st and 2nd editions were loosely based on D&D, 3rd edition adapted the Universal Table from Marvel Super Heroes RPG, except for Gamma World 3e it’s called the Action Table (ACT). This version introduced Mutated Plants as a character type, character level advancement, and organized equipment and weapons by tech level… and Wow! So much more equipment to drool over. More developed races, cryptic alliances, and background information in general. Following this set are 5 linked modules forming a campaign.
Gamma World 3rd edition detailed at Wayne’s Books RPG Reference

I GM’d GW3e back in the old days. The ACT table had a learning curve, but once you got the hang of it, and memorizing the differences between RF (Result Factor), RS (Result Shift), and CS (Column Shift? I believe)… I recall it was a slick system with degrees of success or failure. The ACT table system had some bugs, but I think overall ACT was an intriguing rules set.
Even if you have no taste for the different rules baked into GW3e, this set has a lot of cool elements begging to be imported into other editions of Gamma World.
And the box art is perhaps second only to GW1e cover, in my opinion. Who’s that menacing pair on the cover of 3e? Gamma World: Nort and Scar
See my photoblog posts on prior sets: GAMMA WORLD 1st ed (1978-82): The Original Post-Apoc RPG GAMMA WORLD 2nd edition (1983-84): 1st ed gets a revision

Gamma World 3rd edition [BOX SET]
1986 … James M. Ward & David James Ritchie & Gary Jaquet … TSR 7010 … ISBN 0880383305
BOX CONTENTS:
• 21″x33″ two-sided color mapsheet, containing three maps.
• Rule Book.
• Adventure Book.
• Reference Book.
• Game Master’s Screen.
• Players Screen, with equipment charts and sample characters.
eBay | Amazon (Box) | Amazon (Book only) | DriveThruRPG (PDF / Reprint)
Note a lot of the eBay listings will be the just the original rulebook, or one of the new reprints. Read descriptions carefully. The box set is now a collector item, with collector prices.
The GW3e PDF is only $10 at DTRPG, and reprint paperback $16. These are your ticket if you just want to play or mine for ideas the Gamma World 3e RPG.
Rule Book
64 pages. TSR 7010XXX1901













James M. Ward is solely-credited with GW3e “New Design”.
The Rulebook is almost entirely given over to the rules set, little background or extras here.
The accompanying Adventure Book and Reference Book go some way toward filling in the setting with monsters and a sample adventure. But you could feel that some things were missing from the rules. TSR felt the same way, and soon after launch released a 16-page Rules Supplement booklet. More on that later.
Given how unfamiliar the Action Table was for Gamma World players, I feel gameplay with the ACT could have been summarized much more clearly and succinctly, and defined all the jargon in one place in the Rule Book.
The addition of Mutated Plants as a playable character I enjoyed. Being a plant is a whole different play style: How you eat, whether you sleep, how you move and communicate, all requires some thought and explanation on the part of the player.
Adventure Book
32 pages. TSR 7010XXX2001



Reference Book
32 pages. TSR 7010XXX1902





All the mutants and monsters get a Larry Elmore sketch (these come from GW2e).
Game Master’s Screen & Players Screen
3-panel screens, TSR 7010XXX1401 / TSR 7010XXX1402
















The Wilderness Map on the Player Screen looked familiar… and I found it on Dungeons & Dragons module CM5 Mystery of the Snow Pearls. TSR was infamous for their incessant recycling of maps and art, and here we go again. Except… CM5 (1985) was first, not GW3e!

The GM Screen has all of the weapons and equipment sorted into Tech levels I through V. All the familiar weapons (Vibro Daggers, Torc Grenades, Mark V Blaster, etc) are here. Then at Tech level V comes the awesome. The coolest weapon in the original game, bar none, was the Black Ray Pistol. In GW3e, they made the BRP the flagship of Tech V! New, alien weapons follow, like the Harmonic Disrupter and the Slither Helix. They are mostly unexplained and mysterious here.
The Map
TSR 7010XXX0701

The poster map is essentially identical to the map in GW2e. Though I did see the date was updated to 1986, so the map got reprinted.
Dice



Some dice from current and past sets. Looks like the early days of GW3e were the waning days of the original TSR dice.
Rules Supplement
16 pages. TSR 7010XXX0501





The Rules Supplement isn’t in all GW3e sets, but most of them I’ve seen had it.
Cryptic Alliances, Plant Mutations (errata and additions), Robots (skills and movement), money & barter, Price Lists, ID Codes, vehicles, general equipment, fixed machinery, and structural hit points.

Those Tech V wonder weapons get more description here in the Rules Supplement.
See Also: