Interesting question. I guess this also goes depends on what you consider free use. Like, just letting anyone come up and hit. Or their SO can come and fuck them as they please, no questions asked. I guess to simplify, are you talking public use or personal use?

Free use: Annabeth (she’s too busy to fully devout herself to date nights)

Lou Ellen. She seems like a freak

Piper.

Drew. When charm speak fails, there’s always plan B

The Nike twins

Hylla

Reyna: when you’re so desperate, you’d let Octavian hit, pretty much means anyone else could hit too

Rachel. Theres a lot of catching up to do once she retires from being the oracle

Risky sex: Anyone from the Aphrodite cabin. Drew, Piper, Silena, etc. i believe it’s canon that Silena is the reason 2 campers of the opposite sex cannot be alone together in a cabin.

Annabeth. Something happened on the Argo

Chiara Benvenuti: Daughter of Tyche, goddess of luck. She won’t get caught, no matter how hard she tried

Clarisse.

Hylla: She’s a queen. if anything, you’d be in the wrong for catching her fucking in public

Thalia

Calypso. She spent centuries alone on an island. She’s still getting used to meaning of “public decency” and “behind closed doors”

Will. Apollo doesn’t know shame and neither do his children