My atb commuter has no rear dropout eyelets for a rack, of course, and I am wondering if there is any kind of system that can hack maybe forty pounds. The closest I've found is the Topeak MTX Beam:

TopeakŪ Cycling Accessories ? Products - MTX BeamRack (V-Type)

...which can take twenty pounds of cargo.
I've looked with some curiosity at my unused disc brake mount holes on my left rear dropout. I suppose it is wild and unreasonable to think about finding and somehow mounting an identical hole-mount on the right side dropout and use them for rack "eyelets", but I guess I just like projects.
It seems I might be restricted to a seat-tube mounting system, but I see no real reason why a system that makes use of the rear stays or dropouts as support structures could not be devised.

There is a company called Old Man Mountain and they make racks which are designed to be mounted using wheel axle, they will fit on any type of bike. I don't know if Topeak makes something similar...A cheap seat post rack is good enough if you don't carry any heavy loads.

Ah. Yes. I had thought of using the skewer, but the axle would be even-better. I'll check out O.M.M. 20 pounds: I'd carry in my scrambler back pack pretty easily. I'd like my rear rack to be able to take up to 40, to take some pressure off my shoulders on long rides (touring) and my big orders at the supermarket.
Thanks for the tip!

Tubus also makes an adapter that attaches to the QR wheel axle and provides an attachment point for regular racks (either Tubus or from other makers):
Tubus Quick Release Adapter

Vinyl-coated clips are frequently used to provide the top attachment points, but they can also be used on the lower part of the seat stays for the lower attachment. But unlike the above adapter, they don't move the attachment point back behind the rear axle and may result in heel-overlap issues on bikes with short chain stays.

Wolf: I contacted O.M.M. to see if their Sherpa rack is available in silver.

Pra: The Tubus adapter looks good, but the two-hole-per-side mounting system (vs one-per-side) would mean me buying one of their racks and a seat-tube mount.
I think that in the name of economy, I might go with this RockBros gizmo rated at 25kg:

Racks - Products - Axiom Cycling Gear

Another possible option, depending on your dropout design, is to drill and tap the dropouts for rack eyelets. I did this on my Redline Monocog 29er, which didn't have eyelets for rack or fenders. It worked well, and I've put thousands of loaded miles on it, including a 3200 mile solo tour with camping load. My dropouts (actually track fork ends) are sufficiently beefy that the new eyelets did not dangerously compromise structural integrity.

I'd have to see what you are talking about. I can not envision this.

Here is the thread in the Framebuilders forum in which I asked about the modification. The opening post includes before pictures.

The track forkend in its current configuration is in the attached pic. It has been well tested with lots of miles and heavy loads. It has given me zero issues.

I'm glad you wrote back, Jayw, because I looked on my dropouts.., and they are drilled! (I feel a little bit like a stooge for not knowing this, since I've had the bike for fourteen years). What options does this open for me?

It means you can install racks and fenders (at least on the rear ). Note that you'll need to be able to attach the rack to the seat stays, also. If your bike doesn't have eyelets for this (it probably does if it has two dropout eyelets), seat post clamps with rack eyelets are available.

Does your front fork have any eyelets? If it has one (per side, of course), you can install at least fenders. A front rack isn't as important for urban utility use.

I think the Tubus racks would be stiffer and stronger than this RockBros rack.

And I've seen adapters that fit under the rear caliper brake bolt if you don't have upper eyelets.

At TheTouringStore.com, you can get the 800 number to call. You'll reach Wayne, the owner, and he has extensive experience with making racks work correctly on all kinds of bikes.

Unfortunately, he's temporarily closed until the end of May. But check out his rack adapter page.

When I ordered my Tubus Logo rack from him, he asked a couple of questions, and immediately knew I needed a small aluminum spacer to fit my rear wheel dropouts, and knew that the rack would easily fit with 40c tires and fenders. Very helpful. So if you can wait to the end of the month, he can probably get you working.

It's often easier to attach the rear fender stays to the tubus rack, instead of the bike frame. There's often a little more room that way. The tubus racks have holes for this purpose (but they aren't threaded, you need a bolt, washer and nut, usually a locking nut with the nylon insert. These are available at your local hardware store. I got the stainless bolt, nut, and washer, and found some 1/4 inch thick nylon spacers that kept the stays away from the rack tubes.

From thetouringstore adapters:
A decent looking seat stay clamp that wraps around your seat stays if there's no eyelets there.

Yes, I know I have to attach the rack to the seatstays. The supplied bars at Old Man Mountain (for their Sherpa rack) I have determined to be too long, but O.M.M. has offered to send me 9" ones, which should fit. The also kindly offered to sell me an unpainted rack (I don't want black). I'm hoping to avoid a seatpost attachment as part of the set-up, because my rear fender's clamp will occupy the area on the seatpost.
The front fork has eyelets on the rear of the dropout, abd I won't be using them for a fender (front fender attaches to steerer tube), so maybe they can be used for a rack. I hadn't planned on using it.

I can send him a picture of my dropouts.
Do you know if they offer unfinished/polished racks?

This is what I use, the Salsa Rack-Lock.
It works well with my Tubus Cargo (and the cheaper aluminum rack it replaced).

There are stainless steel racks, and even titanium racks. But you'll pay extra for these. The Ti rack is about $300 instead of about $150 for the painted steel rack.