I'm not author of this mod. This is edited copy to work with Factorio 0.15. For 0.16 read below.

I'm complete newbie dumb in lua language. But I fix original version of this mod to run with Factorio 0.15. And it runs well (for my short testing).
My other tries of editing this mod to run it in 0.16 are fail. :(

DESCRIPTION:
A mod that adds 36x36 "factory buildings" that you can enter and build inside of. A HEAVILY optimized from-scratch replacement for Factorissimo!

IMPORTANT:
This mod deserve his update to 0.16, because his perfomance IS OUTSTANDING! Comparing with Factorissimo - Free Real Estate is about up to ~30 TIMES (!) more efficient with doing the same job in about 100 factories! It's true, because my old notebook is very sensitive to high CPU loads and I measure it. Author Sirenfal is really done a great job, but mod needs to be updated. PLEASE, great Lua coders! Believe me, we need this mod to 0.16. I tried my best for a long time but I fail... Sorry, because I asking for you. Please, masters of code, relive this masterpiece to 0.16!!! We can't wait for this! Pleeeeaaaassseee...

Here is link to pre-0.16-FreeRealEstate, https://ufile.io/2cwg1 - in this edit - game can now load, new game starts, factories can be builded, but when player wants to enter in - ERROR - "while running event Free_Real_Estate::on_picked_up_item (ID5) Free_Real_Estate/factory/waypoint.lua:148: attempt to index local 'transit' (a nil value)". That's all my friends. Help!!!

and sorry for my bad English(

Here is original README from author Sirenfal:

Usage

How do I enter a factory?
Walk near the door (or factory exit) and press your pick up item key (default is "F").

How do I get started once I'm inside?
Click on a selector on the left, top, or right wall and choose an item, circuit, or fluid input or output. Then hit the green refresh button on the left side of your screen to spawn your selected choices.

IMPORTANT NOTES

Factories are not intended to be placed by construction robots. It should be impossible, but if another mod forces them to be placed expect undefined behavior.
I highly suggest using this with add-Loaders and/or Bob's Adjustable Inserters since item throughput is limited by how fast you can put items into and out of chests.
Fluid relays do NOT exert any pressure in any direction. They are, on both sides, just storage tanks. This is intentional. If you want to move fluids you need to use pumps.

How is this different from Factorissimo?

This mod was written from scratch and performs a lot better, but since I redesigned the mod from the ground up with different ideas many things are different.

The main differences:

There is no way to produce power inside a factory and relay it outside. (Factorissimo's "power plants")
Players can no longer be inside a factory when another player has picked it up.
Buildings inside factories will not function when a factory has been picked up.
There is no limit to the number of factories you can build. (Factorissimo was limited to 255, and would corrupt your save afterwards)
Factories perform better, so you can use a lot of factories without lagging your map. Performance is directly related to how much stuff is moving through relays into and out of factories. Fluid and circuit relays are much faster than items, but even items are very fast.
Factories are a bit more expensive and complex to make.

What features does this mod have?

Works in multiplayer.
Item, fluid, and circuit relays to move things into and out of factories. These are directional, and can be configured from inside the factory.
Pollution will be moved from inside the factory to wherever the factory has been placed.
Factories can be placed inside factories if the recursion setting is enabled. This was disabled by default.
Factory relays can link directly to each other. (If you place two factories touching each other their relays will link to the relay at that position in the other factory) ***-this in not work for now, until being fixed for 0.15 or 0.16 :(
Circuit relays allow you to send signals in and out of factories. (These run once every 2 seconds)
Item relays correctly respect the "bar", the red X you can use on chests. If you set a bar on an output the input direction won't keep sending items you don't want.
Fluid relays properly mix temperatures.
Factories can be renamed. Names will show both on the building mouseover. (see here) and on the item tooltip when picked up.
Factories which are empty will be un-named and will stack back with normal un-placed factory items.
Several configurable settings. (see config.lua)

Can you add support for other factory sizes?

Support for other factory sizes is already done, but I haven't decided what sizes to use and I don't have graphics for other factory sizes. I'm open to suggestions. Recipes probably need tweaking too.

If you're absolutely desperate for another factory size you can edit the FACTORY_SIZE constant at the top of the factory\factory.lua file. Changing this on an existing map should be safe, but you should back up your save first just in case. If you use it on an existing map factories that have already been placed will use the old size, and new factories will use the new size.