I have designed a modification for dolphin7. Since i dont have much identity with boonex, i cant deliver my product to the boonex users. If you are interested and wish i will provide you the screenshots.
You can use your blog on ModMySite.Com as a marketplace.

Blogs are here: http://www.modmysite.com/blogs/

There you can describe you modification, and post screen shots (links) and so on.

You can also make a "custom page" if you want your product to have it's own "page":
http://www.modmysite.com/blog_usercp.php?do=custompage

Then, link to it from your blog, or forum posts (or your signature).

Warm regards,

Smoge