Ditto on Flexible Survival. Don't let the whole "special program" thing scare you off though; it's like saying you need a browser or flash player to run a flash game. You just need to know what to look for is all.
I would recommend using WinGit as the interpreter. I've tried Gargoyle and Glulx as well, but WinGit was more stable and faster to run. Link to the game is below. If you already have an interpreter of your own installed, you shouldn't need to run the MSI installer and should only need the Flexible Survival file by itself. Clicking on Flexible Survival lets you download said file, which will be a .GBLORB file type. The game is pretty big (one of the biggest in terms of writing and scene diversity I've seen ever), so it can be daunting at first, but you'll start to have fun with it once you're used to it. I would start in Researcher mode first to kind of test the waters since that's the closest to a sandbox, no-time-limit mode you'll get. Normally, the game has a turn limit, though some actions and moments of progress net you extra time.
The only downside to the game is that, despite the sheer amount of writing, enemies, locations, NPC's and such, it does still tend to seem unfinished in many areas and even uncoordinated (some enemies don't even have sex scenes)...that and I still haven't seen a lot of reasons besides literally a few unique scenes to be strictly male or female if you can be herm/futa/what ever, most of the time being a herm gives you both male and female options.
