Roman Evaluation is a consensus decision technique designed to get a proposal past Violent Agreement, focusing attention on the parts of a proposal that need clarification or modification, and driving it towards an agreement that all will support. The technique works as follows:
At some point during a discussion, someone makes a proposal ("I propose...") and calls for a Roman evaluation.
Participants give a thumbs-up (yes), thumbs-down (no), or thumb-sideways (will abide by the group's decision).
Those who voted thumbs-down are given the opportunity to seek clarification, air their concerns, or propose modifications to the proposal.
The group discusses the objections, possibly modifying the proposal. If serious problems were surfaced, the proposal may be abandoned, and discussion continues. Otherwise, the proposal is voted on again.
The vote-discuss-modify cycle continues until there are no thumbs-down votes, or until it is clear that the proposal won't fly.
I've found that decisions reached this way tend to stick. The proposal is explicit, reducing the chance that people will later discover that they agreed to different interpretations. There's little room for steam-rollering, so minority objections don't get forced underground. Everyone who feels they need to be heard has a chance to speak. Allowing people an "agree to abide by" option both eliminates the need to vote no if they can't vote yes, and reinforces the process by letting people put their trust in the group. Done right, it's both quick and a great way to get an unfocused, stuck discussion back on track.
Roman Evaluation is based on a technique taught by Gerald Weinberg, with some local tweaking.
-- Dave Smith
The Apache Group uses a similar system for considering technical proposals. From dev.apache.org 
:
+1 Yes, agree, or the action should be performed. On some issues, this vote is only binding if the voter has tested the action on their own system(s).
0 Abstain, no opinion, or I am happy to let the other group members decide this issue. An abstention may have detrimental effects if too many people abstain.
-1 No. On issues where consensus is required, this vote counts as a veto. All vetos must include an explanation of why the veto is appropriate. A veto with no explanation is void. No veto can be overruled. If you disagree with the veto, you should lobby the person who cast the veto. Voters intending to veto an action item should make their opinions known to the group immediately, so that the problem can be remedied as early as possible.
An action item requiring consensus approval must receive at least 3 binding +1 votes and no vetos. An action item requiring majority approval must receive at least 3 binding +1 votes and more +1 votes than -1 votes (i.e., a majority with a minimum quorum of three positive votes). All other action items are considered to have lazy approval until someone votes -1, after which point they are decided by either consensus or a majority vote, depending upon the type of action item.
-- Martin Pool
Historical trivia: In Gestures, Desmond Morris points out that the meanings of these gestures have been corrupted over time from the Roman usage. When judging vanquished gladiators, pollice verso (turned thumb) meant death, and
pollice compresso (fist with thumb hidden) meant spare the gladiator.
Isn't that the meaning described above? "death to that proposal"?
Not quite. Thumb up meant death.
The reason for this is not hard to find. If they wanted the victorious man to plunge in the sword, they mimed the act with their hands, their extended thumbs stabbing the air in encouragement.
I was taught at school that no one knew which thumb up or down meant which... can't believe its really solved since so I'll ask for a source??. Thumb up is more like a disembowelling action though, I agree -- Andrew Cates
The "Decider Protocol" from The Core Protocol of the Software For Your Head book is similar: One can vote yes, abstain, no, or "absolutely not." Having discussed an issue and called for a vote, only the "no" voters can talk. One at a time, they must say what change to the proposal would cause them to vote "yes." The proposal should be refined until there are no "no" votes. One "absolutely not" vote is a veto and breaks the team out of the decider protocol. One can talk with the person(s) and make another proposal, however.
Wouldn't this be more complete if it included "absolutely yes" and "mu"? (To forestall the notion that "mu" is subsumed under "absolutely not", "mu" needn't mean veto nor a desire to (permanently on the issue, I presume) break the team out of the protocol. "Fire!" is a kind of "mu", after all. More typical "mu" would be that the wrong subject is being decided, so I suppose that falls under "break out of the protocol", but for that kind of "mu", and also for the "absolutely not veto", what happens then outside of the protocol?
Related patterns: Roman Hands, Russian Fingers, The Core Decider, Category Voting.
See original on c2.com