B4R is free and the framework is open source.
V1.20 (currently in public beta) adds support for ESP8266 boards: https://www.b4x.com/android/forum/threads/b4r-v1-20-beta-support-for-esp8266-boards.68213/#post-432723.
B4R includes a modern IDE, lightweight framework and all the tools needed to develop native Arduino and ESP8266 solutions. The programming language is similar to Visual Basic.
Example: