Is there a website for sharing solutions to exercises in math books? I'm self-studying math and I find solution manuals like this very helpful. When I do an exercise, I usually scribble down a few lines (sometimes I don't write anything at all), then look at the solution and if I see the same idea as mine, I'm convinced that my proof is correct or at least I got the right idea. If my proof is different from proof given in the solution manual, I write it down in great detail to verify that it's correct. This takes a lot of time.
Unfortunately, few books have solution manuals. For example, "A Course in Algebra" by E. B. Vinberg is a very popular book in my country, but there is no solution manual. It's a pity that a lot of people do exercises from this book every year and their solutions just go to a trash can.
Solution manuals save a lot of time and provide some degree of comfort. It'd be nice to have a website with search by title and author, where people would post their $\LaTeX$-formatted solutions to each exercise and vote for best solutions. My question is whether such a website exists and if it doesn't, why? Is there any legal or pedagogical reasons?