You don't need a login for Wikidiagrams. You can will be able, soon, to use the Design Forge to create diagrams without having an account.
I'm unsure how to fund Wikidiagrams development. Wikidiagrams needs funding for it to thrive. My Patreon is one approach.
I am not sure what else to try. One possibility is that at a future date I make Wikidiagrams freemium, a free part and a premium part. The 'Design Forge' part of this site would remain free to use for designing, but would have two plans. The two plans on offer would be:
On the free plan, you'll be able to make diagrams completely for free. However, if you also want to store your diagrams on my server then you'll need the subscription. It costs me to provide the server at all. I wouldn't be bothering with doing the persistent server storage too, except as a way to fund my Wikidiagrams work.
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