Below are some ideas for free standing bases.
EMT Fitting Direct to Wood or other (1/2 NPT Threads)
Mounting Flanges to 3/4" wood base or other
Plastic Plates - plastic plates with 7/8 hole drilled in middle or offset. The plates will need to be stiff to support material loads or reinforced underneath with wood or some other material.
Cake pans./Pizza pans - drill 7/8 hole -- thrift stores or amazon for cheap.
Round Saw Blades - Most round saw blades for circular saws, chop saws and grinders have a 7/8" hole. that may make for wonderful system for used products. A used diamond tile saw blade would be ideal as there would be no sharp edges. will need some little spacers / feet. The thick grinder blades with offest are actually perfect. i only have them in a 4-5" . need in the 8-10" range and not sure they have the offsets.
X frame - some type of very simple x frame. Wood or ACM or pipe fittings like a flat tripod
H Frame - some type of very simple x frame. Wood or ACM will try first
Tripod - some type of trypod. not coming up with anything easy yet
EZ Bake oven - I'm trying to figure out how to make a pancake with some concrete in it and a fitting that gets baked in. Could paint or dye it when done. (or put concreate in plates?)
Lamp Bases
this only works with a thicker plate than we have sourced or with other support below the plate and the plate is used as a cover.
This is the particle board shelving with a 3/4" hole drilled and hollowed out just slightly and a 1/2" EMT fitting was then treaded into the hole but requires a little finesse. You can not use a 7/8" bit to hollow out as it is too big. Having a 1/2" EMT tap may be good for his if you want to to it regularly. We have not found any "inserts" for 1/2" NPT.
This has worked well for 1 monitor systems. It has also worked for 2 Monitor Systems.
Bellow is the same system in 2x material for a 1/2" EMT Fitting. Tools shown include: Drill, 7/8" paddle bit, 1/2" EMT Tap, 17mm socket to drive the tap and wrench to turn fitting into hole.
A 1/2" or 3/4" Floor Flange mounted to a 3/4" thick or thicker wooden base or other is a straight forward solution with the least components. The problem with 1/2" wood or less is the lack of space for screws to properly bite the wood without goign through. 1/2" can likely work with proper screws and thought but anything less would not, unless you tried to com up from the bottom and countersukc screw heads.
5 way fittings offer an option for 4 legs and a post. Even if you only want to use 2 legs or 3, it's likely best to buy the 5 star and just not use 2 unless you are really concerned about aesthetics.
1/2" PVC with nub sticking up and 3/4" PEX busing for top half of 3/4" coupling
can cover pieces with plate if they are short enough...
https://www.amazon.com/Zernmiarder-Fittings-Fitting-Furniture-Connectors/dp/B0D9YLFJ8T?th=1
this is a 3 way fitting
https://www.amazon.com/dp/B0D9YKZ42R/?th=1
This is a 4 way fitting...
This belongs on a floor mount page. it's a large system. However it provides an idea for another type of desk moutned base with bent legs
https://www.amazon.com/Matthews-Stand-SPUD-Adapter-Chrome-Plated/dp/B0F25DBQSV
1 1/8 to 5/8 spud adapter