This is a list of EOS sidechains I am aware of so far:
EOS after its mainnet launched was criticized heavily for having poor token distribution. A very large share of tokens were in the hands of top 1000 wallets. Also, Block.One's year long ICO was criticized for unfairness. Some users brought EOS at 45 cents and some others at 17 dollars.
The Telos fork plans to solve the distribution issue by making the airdrop more fair to token holders who have low amount of EOS in their wallet.
Claims to be the blockchain's financial district. I have heard bad reviews of it from my whale friends who brought it at ICO price. They have an active airdrop to EOS holders but you need to do KYC to get the tokens.
3. Insights Network
Insights network launched their own instance of EOS.IO as Instar Blockchain. I haven't had the time to study what they are planing. Learn more about them from https://medium.com/insightsnetwork
4. Uno Social
Uno Social is a social network application utilizing EOS.IO software. It's primarily targetted towards the chinese market.
WAX stands for Worldwide Asset eXchange. It's an e commerce based blockchain for trading virtual items. Read more about WAX here: https://wax.io