Having an off day, let’s try out this meme from birdsite! One like equals one answer (unless I feel really ambitious).
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15. This is an interesting enough question to answer on its own, since I basically *started* with homebrew content.
Almost universally as kids, we discarded AD&D's stat limits for women, the table for weapon types vs AC, and any idea of the DMG to-hit or saving throw tables being off limits for players. A house rule *everyone* used was allowing a player one 18 stat - everything else was rolled randomly - and most people allowed single-class non-human characters to gain levels indefinitely.
When 2e came out, I was in a hybrid game for a while which used some of Unearthed Arcana's rules since we weren't that well off and getting new rules books was a slow process - I played a cavalier.
By a different definition, though I've never been in the definition "homebrew" where people used D&D rules to create a completely new battery of wildly different races or class options (f'rex, trying to make Middle Earth, the Wild West with animal people, etc).