Add Flex from YC research

[Flex](harc.ycr.org/flex/)

README.md

@@ -188,6 +188,9 @@ Join us on slack at [**#awesome-explorables**](https://awesome-explorables.com/)
 * [Lively Kernel](http://lively-kernel.org)
 * [Coeffects](http://tomasp.net/coeffects/) - Context-aware programming languages
 * [INFO 3300 - Data-driven Web Applications](mimno.infosci.cornell.edu/info3300/)
+* [Flex - YC Research](https://harc.ycr.org/flex/) - Interactive programming and solution exploration tools
+  * [Ohm](https://github.com/harc/ohm) - Visual parser generator and toolkit for building interpreters and compilers.
+  * [Chorus](http://www.chorus-home.org) - Visual mobile programming using spreadsheet concepts
 
 
 ## Books