BossShopPro is one of the most player-friendly and multifunctional GUI plugins ever! Say goodbye to all the annoying command- or signshops! It can not only be used to create shops but for every kind of menu. Here are just a few examples:
More information about the project can be found here: Link. The page includes a download-link as well.
A few notes regarding building BSP: the current state of the code, unfortunately, requires you to manually add (the jars of) a few other plugins to the project in order to be able to successfully build BSP. As BSP includes support for many different plugins, such as Kingdoms and EpicSpawners, you need to add those to the project (at least those, which I was not able to add directly via Maven). It requires some initial effort to download those plugins and add them to the project.
One (in my opinion a dirty one) workaround might be to just remove the code of those plugins you do not care about anyways, skipping the step where you have to download the jars. This has been done by a few people already. Without having tested the code myself, here is a commit of a fork, where it was already attempted to remove that code: https://github.com/Megumiovo/BossShopPro/commit/319e8c13dfab33b73c1856428e638d1bc1b63698
Information regarding the BossShopPro API can be found here: Link.