AntiPVPLog is a plugin designed to stop people from logging out to avoid combat without changing any non-pvp gameplay. When logging out you will spawn a skeleton with your armor and health that can not attack. If that skeleton dies it will drop your inventory and the next time you log in you will be dead (Without dropping any items a second time).
The source code is available on github.
How can I log out safely?
The /logout command has been added which will kick you from the server and not spawn a skeleton that can be killed. It will be cancelled if you take damage or move, similar to many MMORPGS.
Can I die to mobs from this?
No. The skeleton can not take any damage outside of getting hit from another real player (This includes fall damage, lava, etc).
How long does it stay there?
The skeleton will last for 10 seconds before safely despawning.
Can I log in and out to buy time for my friends to get there?
You can, but each time the skeleton takes damage it will subtract that from your health upon logging back in too.