(I did search and couldn't find any threads similar in topic) Interested to see what other Fantasy games people know of, or play, other than the official Games Workshop systems. Some I know of are - The 9th Age (version 1.1 being before they strongly changed the direction to distance from GW) Probably the best known continuation of WFB, after version 1.1 they moved away from GW rules and fluff a lot. Warhammer Fantasy 8.5, an effort to just do minor tweaks to 8th to smooth out any OP/rough edges. Warhammer Armies Project, "9th edition" rules and army books. Also tweaked/updated army books for 8th edition, I assume to try to balance them a little more. Warlords of Erewhon, Rick Priestly has fun making a Fantasy army/skirmish game using systems similar to Bolt Action etc. D10 based game with 0-10 statlines, a randomised lucky-dip unit activation system, morale taking a big factor. Very fun written rulebook, really has that classic WFB feel to the writing, Rick wrote up army lists so people can use basically any generic fantasy miniatures they own to enjoy the game. (The rules just for goblin fanatics is two full pages for goodness sake!) One Page Rules Fantasy, super simple rules for quick and easy games using generic GW style fantasy armies. Also comes in 40k, skirmish and rank-and-file flavours. Out of all of these this is the easiest to check out and play by far! Warmaster There is a fan continuation of Warmaster rules, I don't know anything about that game system but it's nice to know it lives on. Easily found with a quick google. I've only been able to play OPR Fantasy so far, and whilst it's excellent for kids and quick games is just slightly too little granularity for my tastes.
Kings of War (by Mantic Games) is another one, but I've never personally played it as I play exclusively 8th edition WFB.
I know of some others: Oathmark: North Star's own take on rank-and-flank fantasy wargaming, in a similar scale of unit size to Warhammer Fantasy, but using D10s instead of D6s and with army-building rules that are closer in style to pre-4th Edition Fantasy (i.e. that you can intermix units from different races relatively freely, as long as you follow their kingdom-building rules). Generally very well-received by the fantasy gaming community and accompanied by some excellent, good-value miniature kits in a range of Tolkien-esque aesthetics, all of them pleasing to me in particular. There are a couple of threads already on the forum for this game here and here. Forgotten World: Fireforge Games' rank-and-flank rules that arrived with their good-quality models for Stark-inspired Northmen and undead a few years ago and also work with their great-looking not-Bretonnia models. For some reason, despite it having been available to buy for a while, I haven't seen any reviews for this game at all apart from the obligatory Wargames Illustrated one, which is incredibly strange given the demand for rank-and-flank games since Warhammer Fantasy was executed. Always worth picking it up if you're able, particularly as their range of Dwarves, the Stone Realm, is due to arrive in early 2022. Additional planned factions include a not-Lannister human faction, Orcs that are as tall as Primaris Marines and generic Elves. Conquest - The Last Argument of Kings: @Sudsinabucket is our main ambassador for this game, made by Para Bellum, in its own unique fantasy world with living lore and particularly interesting factions, with unique aesthetics and none of them being inherently purely good or evil. Looks a fun game, the only thing is that the scale for the models is significantly bigger than 28mm, so if you want to get into it you can't really proxy other models to represent your faction of choice unless you and your opponent don't mind fielding armies of relative midgets. War of the Ring: The mass battle counterpart to the Middle Earth Strategy Battle Game - I know it may account as an 'official' GW system, but I still listed it here given that GW ditched it in 2012 and it's relatively little-known, which I do think is a shame because now there are no official rules for proper mass battles in Middle Earth, as the Middle Earth Strategy Battle Game feels more like skirmish ruleset and is purposefully written to work at relatively small points values, compared to War of the Ring which was more like Warhammer Fantasy (and was probably executed because of its similarity and similarly high entry cost). If you can find a second-hand copy it'll certainly serve you well (I played a game of it once and really enjoyed it) and the 'One Ring' forum has been keeping it alive with errata and rules for all the new Middle Earth units that have arrived since the game officially died. A Song of Ice and Fire Miniatures Game: In case you didn't guess from the title, Game of Thrones fantasy battles. Again, a solid-looking game with good-quality miniatures from CMON (unfortunately they're ready made so you can't alter the poses unless you're willing to make some limb swaps, but it's good if you're not so into the building side of the hobby), with aesthetics imagined from the book series rather than the TV series (not necessarily a bad thing, you can always use your imagination to meld the Tyrion model into Peter Dinklage, for instance). I must say the game is doing very well at fleshing out unique army lists for the different factions and giving them all different aesthetics, which isn't particularly easy given GoT isn't the most 'fantastical' of Fantasy settings. Runewars: Fantasy Flight Games' own attempt to stray into mass fantasy battle territory, set in their own fantasy world of Terrinoth, with four different factions - a Warcraft Alliance-style human faction, an undead faction, a Wood Elf faction and a faction that's a hybrid between Tomb Kings and Tyranids. Sadly they've cut off all releases and tournament play for this game, but I imagine it's still possible to get the models and rules somewhere, even if second-hand is the only way to go.
Sorry, I'm 8th Edition only. I tried getting into 9th Edition a couple of years ago but I just couldn't warm to it.
Another couple I've just thought of: Dragon Rampant: A warband-level Fantasy game like Warlords of Erehwon written by the creator of the similar Medieval ruleset Lion Rampant. Never played it but it is an Osprey ruleset and those are always decent. Battles of Westeros: As Warmaster has now been added to @PlasmaDavid's list, I thought I'd might as well add the GoT equivalent alongside it! Again this game takes artwork and miniature design from imagined depictions of the books rather than scenes and characters from the series, and like Runewars it's an FFG creation they seem to have got tired of, but to be honest it looks the best of their GoT creations and any fan of Mr. Martin's universe will probably have a lot of fun deciding the outcome of truly massive battles for the Iron Throne.
I would add Mordheim, even though technically it is GW in origin it is no longer supported by them. Also Frostgrave and Ghost Archipelago! Essentially the same two games (skirmish-warband-campaign style games) with two different flavors of icy-wintery-ruins and jungle-island-ruins respectively.