There are a large number (almost 600) FRUA designs archived here : http://frua.rosedragon.org/modulelist/file.php

To use a non-hacked design (see below) all you need to do is create a folder for it in your Unlimited Adventures directory that ends in .DSN (so, SOMEGAME.DSN for example) and extract the files from the design into it (make sure you don't have nested .DSN folders, depending on how the design was packed.)

For hacked designs (designs that use editors to change out things that normally can't be modified through the FRUA interface) you will need UASHELL, which is a batch file and set of executables that "Apply" the hacks for a particular design. Instructions on installing and using UASHELL are located at : http://ua.reonis.com/index.php?topic=464.msg1180#msg1180

This thread should be pinned. I've known about FRUA Archive for a long time and it makes Unlimited Adventures an even greater value.

There is one other site to consider, though only a few mods are there. Darius' Unlimited Adventures Domain at: http://ua_domain.tripod.com/index.html

Reviews for most of the designs can be found here: http://ua.reonis.com/index.php?board=5.0

Not just one, apart from Darius a few other prolific UA authors have their own websites, too (e.g. Ray Dyer's Realm campaign & Goldbox remakes or No Drek's UA page, and Nol also made a page for Super Hero UA). But all of these games are available from the UA File Archive too.

I've created an extensive sticky about FRUA for the GOG forums, I hope you guys don't mind that it also repeats the links and instructions that Krebbs posted above.

The instructions for hacked designs start by assuming the game is running under DOSBox on a Windows PC. What if my PC isn't running Windows? (In my case, it runs Linux exclusively.)

What's the difference? Can't you just run DOSBox under Linux, too? Or did you mean my instructions from the sticky, about using D-Fend Reloaded? In that case, you'll have to search for a different frontend that's compatible with Linux (maybe D-Box? I'm not familiar with it, but it's compatible with Linux) and then figure out how to use it yourself. The general instructions should remain the same.

Sorry for my ignorance, but I only have experience with Windows. You could try posting your question on the UA forums, there might be one or two Linux users over there (possibly among the Dungeon Craft crowd). Just be patient, the forum isn't as lively as this one, so it could take a day or two until you get a reply.

I've updated the installation guide for hacked designs to include instructions for Linux users, kindly provided by member joeshell. Hope that helps!