Any particular link may not be to your taste. Proceed with an open mind.
Sites that cover multiple topics, or there is only one site on a specific topic. Difficult to categorize these so they are all here together.
Buttplug – “an open-source standards and software project for controlling intimate hardware, including sex toys, fucking machines, electrostim hardware, and more.”
A Fetish Leathercrafter’s Journal – Lots of info including tutorials, photos and downloadable patterns. Not particularly well organized so you kind of have to click around a bit or just go through the archives.
Université de Genève’s Teaching Tools – 3d printable models of male and female genitals and reproductive organs. “We are developing a teaching kit (web platform, 3D models, etc…) for health professionals, sex education teachers, and school teachers around sexual anatomy, physiology and histology .” From the same authors there are diagrams and scholarly writing on the subject mostly of female anatomy especially the clitoris. (Mostly but not entirely in French) Clit’info – a website by same authors with lots of info on the clitoris (French only)
Domina’s Shopping and Home Manufacturing Tips – Classic website with instructions for a wide array of BDSM and sex equipment. One of the first websites on this topic.
OurDollComunity Forum: The Workshop – Sex doll DIY.
Fashion Incubator Tutorials – Not specifically kinky. How to properly design different articles of clothing. Useful for leather, latex etc.
Disability After Dark – Podacst hosted by Andrew Gurza, a gay man with physical disabilities. About sex and disability in general but the topic of sex toy design is frequently discussed.
tutorials for a single project
Homemade Sex Toy Vagina with Best Hands Free Masturbation Techniques (watch on invidious) – Short YT video for people with penises who enjoy penetration.
anus.org J Lube FAQ – J Lube is a lubricant that comes as a powder and you mix it up according to your preferences. It is famous among gay men as one of the two classic fisting lubes (the other being Crisco). This page contains recipes.
Sex Toy Collective Dildo University – instructions on what you need to know to make silicon insertables.
Sex Toy Collective Dildo Sculptor – “This tool helps you design and print dildos with a 3D printer. You can use the prints as models to cast molds.” Browser app
Newart forums – Active community interested in pumping. Lots of discussion on DIY pumping equipment and related. Primarily this is a body modification community with many people DIYing that.
Sun Tea Jar (STJ) Cylinder – A pumping device popular on the above site. Especially, but not exclusively, for those whose needs surpass the volume of commercially available devices.
SmartStim – estim enthusiasts, many of who make their own toys, tools, equipment, audio tracks etc. Requires user account to see content. Sometimes registration is limited, or must be manually approved; patience required. Another website warns: “beware of anti-social and condescending administrators and moderators when asking questions or responding to topics. Not highly recommended but it exists.” but that hasn’t been my experience. Forum has been around a long time and has lots and lots of info.
Social Stim – supposedly another e-stim forum (I couldn’t get registration to work).
zity.biz forum DIY electrodes and devices – not fantastic but you might find something of value.
reddit.com/r/estim wiki – has info on DIY as well as all other aspects of estim
sexEstim – a blog about DIY e stim. Also discusses history and philosophy of stimming. Collection of documents, books, magazine articles, scholarly articles etc that could be of interested to DIYers. (Mostly Russian.)
Electricity for Pleasure and Pain by “Uncle Abdul” – Scan and transcription of book from Greenery Press. Includes DIY. (Hosted on previous website.)
Joanne’s Reviews: DIY e-stim equipment – Detailed instructions, including 3D printer files, on making DIY e stim electrodes for people who have penises and people who have vulvas.
JG Leathers – A guy in Vancouver who has made some pretty intense sex items for himself. Includes photos, diagrams and extensive writing. Leather, bondage, predicament bondage, gags, insertables, sensory deprivation and much more.
things people have made, or are making, that don’t go to any effort to explain how to duplicate work.
Steelwerks – Montreal workshop making high end custom steel toys, primarily chastity devices for cocks.
transthetics: The Bionic all-in-one super realistic penis prosthetic – “The Bionic is an all-in-one, super realistic prosthetic penis that mimics the natal male genitalia as closely as possible across four functions: pee, pack, pleasure and play – and over two states: flaccid and erect.” FTM (female to male trans) packer (prosthetic cock) being developed with a variety of innovative technologies. Unfortunately does not seem to be open source.
A Failure of Academic Quality Control: The Technology of Orgasm (PDF) – 2018 scholarly paper in the Journal of Positive Sexuality which debunks the oft-repeated myth vibrators were used by Victorian doctors to treat “hysteria”, and more interestingly, goes step by step through the process of how an academic career was made based on constructing it.
The Huge Dildo Home Page: Where To Get A Huge Dildo (wayback machine) – This was at hugedildohomepage.com but the site doesn’t seem to work anymore. It is a mirror of a geocities site from the 90s about how to jimmy huge dildos when none were available readymade. The DIY information is not fantastic and out of date, but it is a part of our heritage.
Strange Flesh (github) – “a sexy, gay, adult beat ’em up game. You play the role of The Bartender, a master of the hypnotic arts and a servant of the bar, Strange Flesh. In the game, you’ll infiltrate the mind of one of the bar’s many troubled patrons, and help him out however you see fit.” Mac/Windows/Browser