Saving Throw Categories + Extra Saving Throw Uses

For ease of use, every character rolls a general saving throw category. Roll d20, higher rolls are better. You're trying to beat a DC; 10 is for “easy” saves, 15 for “moderate” saves, 20 for “difficult”, and 25+ for anything even more extreme. Every character just adds their general bonus to the roll, which is increased at even levels for core classes + wisdom modifier. Certain specific circumstances may add modifiers; if you're wearing heavy leather boots then you might add their AC bonus to avoiding a snakebite. If you're dodging something, then add your dexterity modifier to the roll, add your intelligence to resist the pain of illusion weapons, etc.

However, each class has a specific bonus they get against specific saves. These three categories are not the only saving throws you make in the game, these are just the specific bonuses each class get.

Combat saving throws are done to avoid the combat tricks of opponents and monsters. Getting tripped by an opponent with a whip, avoiding getting disarmed, and so on. Fighters get a bonus.

Hazard saving throws are done to dangerous terrain and environmental hazards. Avoid falls, keep your balance, dodge traps, avoid hazardous environmental threats and so on. Rogues get a bonus.

Spell saving throws are done against the spells and magic of enemy spellcasters. Resist spells that ensorcell your mind or polymorphing you into a harmless animal. Sages/Mages get a bonus.

Sometimes saves overlap or they are counted as a different category. For example, a magic user conjuring tentacles to tie you up would probably be a combat roll to avoid getting entangled. If an enemy throws caltrops at your feet, that would probably be a Hazard to avoid it, instead of combat.

If you use Clerics in your game but what a Manse spin on it; have them get a bonus every odd level as Save vs Death and level drain.

More Saving Throw Uses

Beyond just saving to avoid something; saving throws could be also used as an alternative to ability score rolls or “skill check” rolls. For example, if your Fighter wanted to grab a manticore's poison stinger tail to keep it from striking his friends, you could have him roll a saving throw, add his Combat saving roll bonus, and see what happens. If your magic user wants to control or manipulate a spell he's already got in progress, let him roll a Spell save to try and change it- this will let him open a hole in his own magic wall of fire so he can pass through unharmed. Because saving throws already have stat and class bonuses; this is useful way to include other actions in the games.