In 2000, at least 991 Nader supporters in Florida pledged to vote for Al Gore in exchange for Gore supporters in other states voting for Nader. These vote swaps very nearly decided the election: the final difference between Bush and Gore was 537 votes.
The 2000 vote swaps were organized through a handful of websites that were rapidly shutdown under legal threats. Since then, it has been determined in court that vote swapping is protected under the first amendment, and vote swapping has re-emerged as a way for third-party supporters in swing states to make their vote count for even more, and for main-party supporters in non-swing states make their vote count for /something/.
If you or someone you know are planning on voting for a third-party candidate in a swing state, you can greatly increase the power of your vote by vote swapping. All you have to do is contact a Clinton supporter you know in another state and suggest a trade. Or a variety of resources exist (see below) for finding voting partners online; these sites generally are limited by needing more swing-state voters, and some have offered 2-for-1 trades for people from swing states, so you can turn your third party vote into two third party votes.
Major vote swapping sites:
https://voteswap.us/ (prefers matching you with facebook friends)
Discussion of vote swapping:
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