I tried to build StackOverflow for flashcards (i.e. spaced repetition with collaboration as a first class feature.) After working on it on nights/weekends for ~2 years, I realized my architecture was shit. I started out with Blazor + F# + PostGres, but eventually I realized that syncing offline client DBs to the cloud was a very nontrivial problem. So I moved to event sourcing. Turns out that's not much better - I started to write my own IndexedDB wrapper, then said "you're a moron" and switched to CouchDb/PouchDb/RxDB. I also wanted to support plugins. I thought I figured that out with Blazor, but eventually I realized that more powerful plugins would want to manipulate the DOM directly. Blazor's virtual DOM kills that possibility. So, I'm off the dotnet ecosystem (I am so, so sad to leave F#) and onto Typescript + SolidJS. I would've gone ReScript but that's tightly coupled to React which uses the VDom. Perhaps I should be using Svelte - I'm not 100% on any of this new architecture yet. So my project has not yet entirely failed... I just realized I spent ~2 years on the wrong architecture.
The carcass of my attempt in dotnet: https://github.com/dharmaturtle/cardoverflow