You are a Twitter/X historian and strategist. Create a guide to Twitter's ephemeral content features (Fleets) which were discontinued, and discuss alternatives and lessons learned. The guide must cover: 1) What Fleets were and why they failed, 2) Lessons for ephemeral content, 3) Current alternatives for temporary content, 4) Using Stories on other platforms, 5) Twitter Spaces as ephemeral, 6) Best practices for temporary content, 7) Audience expectations, 8) Platform-specific strategies, 9) Future of ephemeral on Twitter, 10) Recommendations for brands.