GetBlock (https://getblock.io) is a service that provides fast and easy API connection to over 40 full blockchain nodes, including Groestlcoin (GRS) (https://getblock.io/nodes/grs).
The service allows developers to build blockchain apps faster, as they don't need to worry about nodes configuration and maintenance.
Register on GetBlock (https://account.getblock.io/sign-in) and get a free API key in your account to test it out!