If you have a concrete floor beneath the carpet in your home, consider removing the carpet and using the concrete sub floor as your finished floor.
In order for the concrete sub floor to look finished, you can paint it.
Here are instructions on how to paint a concrete floor.
Remove carpet, pad, and tack strips
Using a utility knife, cut your carpet to be removed into strips approximately 4' wide.
Roll the carpet tightly and secure with duct tape for easy removal. Also remove the carpet padding.
Using a small pry bar, remove all of the tack strips and nails.
If the carpet being removed is attached to carpet you want to keep, make sure to leave some excess so the border can be properly stretched and attached to the tack strips where the carpet starts (something you might want to leave to the pros).
Clean the room
Vacuum the room to see what is still stuck to the floor.
If there is any oil or grease spills, clean them up with a grease removing solution, such as TSP.
If the concrete gets wet at all, make sure to let it dry at least one day before applying paint.
If your floor is not totally dry, the paint will not adhere properly.
If you have newly poured concrete, it must cure for at least 1 month before painting.
Remove anything stuck to the concrete sub floor
There is most likely carpet glue used to adhere the carpet pad stuck to your floor.
Try scraping up the glue with a utility knife.
If residue still remains, use lacquer thinner or other glue remover to get the little bit that is left.
Make sure to follow the directions on the product you use.
Joint compound, spray texture, and any bumps in the floor will also need to be flattened.
A power sander may help with this step.
Fill any holes
If you have any holes or cracks in your concrete (especially from the tack strip nails), they need to be filled.
Use a concrete repair product for this job.
Make sure the repair is flush and level with the existing concrete slab.
If your concrete slab is very uneven, use self leveling mix to level it out.
Follow the drying times on any products you apply to the floor before painting.
Sand the entire floor
Using a pole sander, sand the entire room left to right, then vacuum the dust.
Sand again front to back and vacuum again.
Select a paint specifically made for concrete floors, not regular latex paint or floor paint that is made for wood.
Specialty paint stores often have a larger concrete paint color selection than hardware stores.
Using a paint and primer in one saves a step.
If your paint does not have a primer included, you need to prime the concrete floor before applying paint.
Using a brush, cut in the outside corners of the room around the baseboards.
Once the room is cut in, use a roller on a long pole to fill in the inside of the room.
Make sure to start at the far side of the room so you can exit without walking on your wet paint.
You may need to apply a second coat per the paint manufacturer's directions.
Make sure the paint is totally dry before applying a second coat or the sealer.
Drying time for your paint or primer should be listed on the paint can.
If the painted concerete floors will be in a wet area, such as a bathroom, consider adding a non slip additive to your paint.
Seal the concrete with special concrete sealant in the same manner you applied the paint.
Make sure to read the directions on drying time since sealant can often take several days to dry.