Wait, is this just stuff created by 4chan users? If so I may have misunderstood so I didn't contribute anything so far. I'll try anyway.
There are a bunch of websites made by 4chan users.
Also, what about all of those guides to media like pic related? There are a million of them.
/ptg/ pastebin and guide to private trackers https://pastebin.com/thLgSkNE https://wiki.installgentoo.com/index.php/Private_trackers
Many, many more guides like this can be found in generals.
Chancoin - crypto made so you can tip people and it is kind-of used. There are regular /biz/ threads. http://chancoin.info/
Netrunner - /g/ web browser http://netrunner.cc/
not sure how actively it is developed
pantsu - public tracker made by /g/ https://pantsu.cat/
CloverOS - /g/ linux distro https://cloveros.ga/
pomf clones were all originally a 4chan thing and they are mostly still hosted by 4chan postershttps://github.com/tsudoko/long-live-pomf/blob/master/long-live-pomf.mdhttps://sites.google.com/site/pomfclones/https://notabug.org/WubTheCaptain/deathwatch-pomf
4chan x - 4chan browser script http://4chan-x.net/
clover - 4chan mobile application https://floens.github.io/Clover/
qtchan - 4chan desktop browser https://github.com/siavash119/qtchan/
TOX - messaging application https://tox.chat/
(they eventually picked up devs from other places though)
oppaitime - private tracker for hentai/jav/h-games/etc, weeb porn both sysops post here http://oppaiti.me/
Underwater hampsters by a 4chan poster. https://hampture.blogspot.com/
I dunno probably a lot of this doesn't count but I'll just put it in here anyway. Sorry if I misunderstand.
There is a lot more stuff if you just go looking aroundhttp://bans.verniy.xyz/https://www.nexisonline.net/4chan-status/
There are a bunch of 4chan IRC channels. Including the official one.
More stuff like this? Am I just posting bullshit? I'm not sure. I can post more if you want, I think.