A lot of people here have been mentioning Postman but my personal go-to has been Advanced Rest Client [1]. It's open source, has Google Drive integration, and seems to have a pretty impressive development rate. For me, it's a definite plus that there isn't a paid tier so the developers don't have any incentive to limit the free product. That said, Insomnia looks like a nice contender and I look forward to giving it a shot. The reuse of variables across requests and the automatic generation of boilerplate request code both look like really nice features that ARC lacks!