What tool to you use to hand scrape a floor?

Certainly depends on what you are scraping off the floor. I used a Warner floor scraper and a heat gun to remove compressed first generation carpet pad (aka waffle pad) off a hardwood floor and found it to be a far superior approach than using the on-line recommendations of chemicals and the like. However, take care not to gouge the wood. It's all in the angle in which you use to handle the scraper.

Roofing shingle scraper.