pokerstove - it's a gr8 free tool. easiest to use for cash games. i should probably use it more often.
i don't know if any free software exists for SNG's. you use to beable to download sngegt for free but i think that website is gone.
sngwiz has a 7 day free trial, i think.
HEM2 and PT3 both have free trails to my knowledge.
generally you get what you pay for. if you play cash then i would use HEM2 and PT3 free trail. once you know which one you prefer then buy it.
sngwiz is a must if you play SNG's imo.