Tl:dr first paragraph on defining "afk", and I'm trying to post what others haven't posted but are still things I've done while afk/idling. The list below is numbered but the numbers don't indicate any matter of advantage/priority, this is for formatting only.

I think most pvm tasks and even wt are in fact not afk but I know sweaties will disagree. If you are at risk of dying, it is probably not worth afking on say a HCIM - especially these people who have new hcim addictions but can't manage to keep their account HC. There are different "afk" styles I suppose. Some claim that things are afk when they kind of aren't, in fact most things are not afk in osrs. I will be assuming "afk" can mean multi-tasking on osrs and outside of it on other computer applications or even osrs mobile. "Afkable" refers to tasks that require little to no screen attention to complete a reasonably rewarding action.

With that out of the way, here are my top things:

1 Chopping Yews/Oaks, chopping teaks in fossil island, Fishing monks, sharks, or karambwans; all extremely low effort and afkable.

2 Arceeus Library magic/rc + alching; semi afk with about 30k-50k xp per hour if alching while semi-idling (if magic lvl is around 70). Ideal on PC with runelite and 70+ magic or 40+ runecrafting in my opinion. Xp rates are higher if concentrating.

3 Easy temple trek/tithe farm - extremely low risk but will need to avoid combat encounters still. Good for idling and doing 1 run every few minutes. This isn't necessarily afkable but definitely a task you can idle and runs are really short.

4 Small harvest Tithe Farm / general farming - Simply do 1-2 rows at a time instead of 5 rows, yielding 8 fruits instead of 20.

5 Low effort construction - Convenient to afk and check back every couple minutes.

6 Gilded Altar/Ectofuntus/Ranging dragons - to simply train prayer at a lower rate but still maximizing xp per bone.

7 Bankstand alching/fletching - Not the most efficient but low effort money maker. If afking woodcutting a lot, you may have thousands of yew/willows to alch. Task alching is THE way but I've bankstand alched a lot, especially on mobile when I was Work At Home during the covid pandemic.q

8 Clue Hunting - Runelite clue hunting is way too convenient to not grind hundreds of clues in desperation for ranger boots/god items.

9 Safespot Cave Horrors for Black Mask / Safespot slayer tasks.

10 Purchasing ores from Blast Smithing ore shop or purchasing molten glass/soda ash from ports.

11 Blast Smith, Smelt glass/Blow glass

-Disclaimer mining tasks below. I dislike mining for afk because it is a quick action but doesn't pay off well when not concentrating. Mining is extremely slow in terms of both xp and rewards that progress your account.

12 Gem mining for mining, crafting, and magic xp if alching jewelry.

13 Mining iron in mining guild/motherlode mining. MLM not my favorite but I think absolutely early it is worth it for some coal if you can't purchase coal. Once you start getting higher mining you get less coal, though. I think from 60-70 mining iron is better, then go back to MLM if desired and get adamant/rune ores - keeping in mind that smithing is more of a grind than mining is in the late game with exception of amethyst.

14 Daeyalt essence mining.

15 Ammonite crabs or Sand Craft combat training. Very afkable and probably one of the few GENUINELY afkable tasks in osrs.

16 Hosidius Kitchen cooking fish with gauntlets.

17 Birdhouse runs - Great to do once an hour and just requires 2 minutes of time per hour.

18 Grinding Favor with certain tasks

19 Low effort, low rate rune crafting mid-tier runes such as cosmics, natures.

20 Running planks in wcing guild - like glassmaking I find planks to be very annoying especially without lunar spells. Without lunars I think it is worth idling and plank running.