Arbitrum One, an Ethereum Layer 2 or Rollup to improve scalability, was launched in May 28, 2021 

Gas Token : $ETH from US$0.05 to US$3.00 depends on the transaction (check with Cointool)

Wallets : Trust Wallet, Metamask (Chrome extension and Smartphone),  Ledger

Bridge : Arbitrum bridge* (withdraw on Arbitrum ecosytem with Binance or with OKX), ...

Blockchain explorer : Arbiscan

Swap : 1inch , Uniswap

Yield Optimiser : Beefy

DeFi dashboard tracker : Debank

Airdroppossible alert (*for people who use the Arbitrum bridge ?)  : $ARB not yet enable

More information and protocols about Arbitrum ecosystem : Arbitrum One

Other ecosystem : Terra ($LUNA), Elrond ($EGLD), BNB Chain (ex-BSC) ($BNB), Cosmos ($ATOM), Cardano ($ADA), Optimism