I just completed a simple link submission system which allows visitors to a ZenCart site to submit a link which can then be approved or deleted by an admin.

I've done this using a combination of:

Custom page
Custom Sidebox

The functionality is very straightforward and while the code is a tad messy I'm willing to hand it over to anyone wishing to develop it further or use it on their own site, it's been tested and works nicely. There is an included installer which creates a new DB table (yourprefix_links) and other than that you'll just need to upload some files and make 2 configurations in php files.