Mastodon, a Destributed, Decentralized Twitter / Weibo Alternative
Official Introduction Site
Source Code
Some existing mirrors, you just need to register and then log in,simply like twitter:
mastodon.social (basically official)

Accessable Mastodon in Mainland China:
mstdn.jp (japan)
https://wxw.moe/
It’s mirror: 1 2 3 4
https://o3o.ca/
It’s Mirror: 1 2 tg
https://m.cmx.im/ (Blocked)
It’s Mirror: 1 2
acg.mn (Not accept public registration)
mastodon.technology (for tech)
mastodon.hk

Accessable PeerTube instances in China:
https://diode.zone/
https://video.ploud.jp/
https://tilvids.com/
(Maybe you should use bilibili.com / ixigua.com in China )

Other Mastodon instances
other peertube instances