Trade+ is a trading plugin for Spigot servers versions 1.7.10 and up. I've decided to open-source it since I don't have much time to work on it anymore.
If you feel like 'donating'/paying for it, you can do so on the SpigotMC resource page: https://www.spigotmc.org/resources/23138/
But if you want to download it from the releases page that's totally fine too.
If you find bugs or want to add features, you are, of course, more than welcome to submit pull requests. Thanks!