I see that Bitcoin has Blockchain.info, Ethereum has Etherscan.io. What about other coins and tokens. Is it obligatory for the given coin/token to have such blockchain exploring site/tool, is it a best practice or a voluntary measure?
All open source cryptocurrency project should have a community which voluntarily elects to support its ecosystem. At the beginning, block explorers for said cryptocurrency project are run on a voluntary basis, but as it gains traction, there will eventually be an economic incentive to provide said service.