A popular homemade laundry detergent is made using FelsNaptha bar soap (or Octagon, or Ivory).
You will need:
1 bar FelsNaptha
2 cups washing soda
2 cups borax
Grate the soap, finely, then mix with the washing soda and borax. At this point I think you can stop and just use a tablespoon full in each wash load. However, if you want a liquid detergent, add your dry mix into a pot of boiling water to dissolve. Pour into a 5 gallon bucket, keep adding boiling water one gallon at a time, stirring after each gallon, until the bucket is full. Stir each day until the mixture stays homogenized. It will have a gel like consistency. Add a quarter cup per load of laundry.
While the Orvus Paste is gentler to fabric, if you have small children or live on a farm, the homemade FelsNaptha detergent is better at removing stains, but you will notice eventual fading of your clothing.