You didn't restrict this to free apps so look at Syncback and Goldsync. To create N copies you simply have it sync to 2 or more places per your schedule.
Note: Edited to correct title spelling.
I want an app that will backup contents of certain folders on my PC; i do not like the monster backup programs that shove everything into a backup file. Rather i want a facility that will keep N copies of my working files, backing them up every 15 or 30 minutes. I have been using QuikProt but it seems it has gone end of life. any recommendations?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic