The main homebrew setting I've been running games in since I started running games, which I've been building on and off for roughly 20 years now, is built with this sort of interaction in mind. It was originally conceived as a "post-Gamma-World" setting, meaning that the idea was that the Gamma World had several thousand years of history unfold, radiation zones cooling off, and various mutant species being eradicated or rising to become as populous and important as the traditional humans and demihumans. I started this in 1st Edition, made some conversions and refinements for 2nd Edition and ran my first full-fledged campaign in that (as opposed to single adventures now and then for the 1E version), and when 3E came along converted and further refined that into the beginning of its present form.
Most cultures of the world are assumed to be at a pseudo-medieval level of technology, as in a standard D&D world, but sages and others with the right Knowledge ranks are perfectly aware that those strange devices constructed of unknown metals, not-quite-metals (like plastics) and other exotic materials aren't magic at all, but instead products of ancient science. Some objects in the setting, like the six Diamond Towers which once contained space elevators connecting the surface of the world with the orbiting Ring Station (still visible in the sky even in the modern day as a thin white band), are obviously technlogical and obviously beyond the capability of present people to create or maintain. Technological ruins are essentially treated as exotic dungeons, much as such places are treated in some video RPGs like the old Might and Magic series- and of course several entries in the Final Fantasy lineup.
Technological items, I've gone to some trouble to "balance" with magic- in that you can find a tech item to do just about anything, but you'll be paying a price comparable to a magic item that would do the same thing. Nearly all tech devices require special Power Cells to work, which are devices in their own right as far as treasure is concerned; also, most tech devices available today require some sort of repairs or jury-rigging to function fully or properly. I wrote up special rules for how energy weapons work, based on rules from Dragonstar and other sources such as the "high tech weapons" suggestions in the 3.5 DMG; all technological weapons are considered Exotic for characters from most modern cultures. They don't tend to get used much in the games I've run, but characters built around using them can be quite handy in a fight and deadly to their enemies. This is partly because I knew going in that weapons using my new rules would find it difficult to compete with powerful magic weapons in higher-level games, so I gave tech weapons a few advantages to compensate- the most important one being that tech weapons tend to have high critical multipliers, such as the "Mag Rifle/Rail Gun" which gets x5.
Finally, robots and ancient computer AIs do exist; I've written up a special "Robot" subtype for Constructs, and made several monsters using it (ranging from a cute little CR 2 Maintenance Bot up to the terrifying CR 40 Death Machine, my interpretation into my 3.5E setting of the old beast from Gamma World). Several of the most memorable adventures I've run for parties in the current incarnation of the setting have involved interaction with ancient AIs that are still functioning. I even made templates for Cyborg creatures, and one for Living Constructs which in my setting represent "androids" or other robots designed and expressly built to look like and blend in with normal living creatures. They've seen play several times, and in one high-level game one of the PCs was actually a Living Construct whose character background was that he'd been deactivated for roughly 3000 years and only recently "woken up."
