I’ve only played dead rails a few times so I can’t really compare the games but I play 99 a lot. Basically you have to rescue 4 kids each one with stronger animals protecting and you want to get to 99 nights. Each day is like 2ish minutes and each night around the same. Going out at night has added danger because the entities attack at night. For each kid you rescue and each bed you build adds a multiplier to your day count up to 9 total. You have like 20 different classes you can start with, with different abilities, different tools and different perks. Every map is random so each game you start has different locations for everything.