The upstream comment by AnthonyMouse mentioned "approval voting or the like"; in that context, ubernostrum's comment about parliamentary democracy is a bit of a red herring.
In the parliamentary system, those third (or fourth, etc.) parties are actually elected and have power, right? While a non-parliamentary approval-voting system would allow people to vote for a third party and also help elect their preferred major-party candidate. That could sidestep the "forming a government" parliamentary negotiation process.
How that would actually look in practice, I'm not sure. Would it actually help those third parties if they get votes but don't get elected? Would third parties be able to "extort" major parties just by offering pre-election endorsements? How many of those third party candidates would actually end up in the legislature? I don't know if it's been tried at scale.
In the parliamentary system, those third (or fourth, etc.) parties are actually elected and have power, right? While a non-parliamentary approval-voting system would allow people to vote for a third party and also help elect their preferred major-party candidate. That could sidestep the "forming a government" parliamentary negotiation process.
How that would actually look in practice, I'm not sure. Would it actually help those third parties if they get votes but don't get elected? Would third parties be able to "extort" major parties just by offering pre-election endorsements? How many of those third party candidates would actually end up in the legislature? I don't know if it's been tried at scale.