This is a rotational play challenge. The idea is that your sims will get everything they need from stores run by other sims in their town. I'm playing with 8 sims, but you can increase or decrease the number as you wish.
Each of your sims will need 2 empty lots -- one as a residence and one for their store. You may bulldoze existing houses and community lots to accommodate your sims. If you have Outdoor Retreat, you can send them to the campground to pick up some things from the ranger's station --a tent, firepit, chair, lantern, and cooler. Or you can set one of your sims up as an outdoor supply store.
No money cheats allowed, but you don't have to get rid of the money you start out with. The basic $20,000 start fund is about right.
These are some suggested stores, but you can have as many or as few as you wish.
1. Plumbing, lighting, and bedding supplies
3. A bakery (also sells tables and chairs)
4. Appliances and electronics
5. Kids' stuff
6. A bookstore (also sells office furniture)
7. An art gallery (also sells easels, wood-working table, and musical instruments)
8. An athletic equipment store (also sells landscaping).
Sims will live at their businesses until they have a child, at which point they will have to move to their residential lot.
Initially, all buildings will be 8 x 8 square, and made with a flat roof. Sims can live either above their stores or in a basement below. Each time your store reaches $50,000 in funds, you may expand your stock, increase the size of your store, add landscaping, etc. Store owners must start with the basics (cheapest toilet, refrigerator, bookcase, etc.)
Sims may get furniture and other things only from the stores, from career rewards, and from the wood-crafting table. Exceptions are made for items which cannot be sold in their stores (planter boxes, for example). Buy mode is accessible to store owners only for what they stock. Sims must start with only one outfit in each category in CAS and buy the rest of their clothing from a clothing store. Sims may not own wardrobes. Sims may have jobs in addition to owning their stores.
This challenge can go on as long as you wish, but one endpoint might be when each of your starting sims has made $1,000,000 in profit.
I have a story based on this, After the Plague on Carl's Forum. The link to my story is in my signature.