Yes, some free slot machine apps offer the chance to win real money. These apps often have in-app purchases or advertisements that generate revenue for the developers, and they might also have a system where you can earn virtual currency or tokens by playing the free slot games.
But, if you do decide to play on casino apps, they have hundreds of slot games available and can essentially be classed as slot apps. Therefore, this means you can play free slots to win real money with no deposit required on slot apps!