alpipego

This plugin adds <a href="https://github.com/jessepollak/card" rel="nofollow ugc">@jessepollak’s Card library</a> to the checkout page of Easy Digital Downloads.
<blockquote>
Everything is created with pure CSS, HTML, and Javascript — no images required
</blockquote>
Check out Jesse’s <a href="https://jessepollak.github.io/card/" rel="nofollow ugc">Demo</a>.

EDD Card

Adaption of @jessepollak's Card for Easy Digital Downloads.

Dan Griffiths

Adds a robust third-party product system to Easy Digital Downloads. When activated, adds new fields to the Download Prices meta box allowing you to specify redirect details.
External Products is based on the extension of the same name by WebDevStudios.

Easy Digital Downloads – External Products

Was looking for exactly this: an option to add third party plugins on my own EDD shop. 

Perfect

Adds a robust third-party product system to Easy Digital Downloads

EDD Card vs Easy Digital Downloads – External Products