I searched so many times about RESTful APIs but I got nothing . Fortunately I found a documents that help me a lot.
https://v2.steemconnect.com/docs/steemjs
In that pages, we can use Try it to try some api
API domain: https://api.steemjs.com
Some GET APIs such as:
Get account info
https://api.steemjs.com/get_accounts?names[]=neversmile12b1
Get content of a post
https://api.steemjs.com/get_content?author=neversmile12b1&permlink=first-post
Get tags used by author\
https://api.steemjs.com/get_tags_used_by_author?author=neversmile12b1
Get block info
https://api.steemjs.com/get_block?blockNum=121212
Get State
https://api.steemjs.com/get_state?path=value
Get config
https://api.steemjs.com/get_config
Get dynamic global properties
https://api.steemjs.com/get_dynamic_global_properties
Get chain properties
https://api.steemjs.com/get_chain_properties
Get witness schedule
https://api.steemjs.com/get_witness_schedule
Get accounts count
https://api.steemjs.com/get_account_count
Get transaction
https://api.steemjs.com/get_transaction?trxId=value
And so so many APIs you can you for your own application, check it out https://v2.steemconnect.com/docs/steemjs