Android Studio is an IDE and SDK for Android developement built on IntelliJ IDEA. It provides various build schemes and APK packaging + signing, rich and context-sensitive editing and refactoring support, GitHub integration, mobile device emulations for debugging, Gradle support, a flexible and multi-screen UI, Google Services and Cloud integration templates, and runs on all major platforms.
dex2jar is a tool collection to work on Android .dex and Java .class/.jar files. dex-reader can extract from executables (.dex/.odex), while dex-translator performs the conversion from dex-IR format, and returns optimized ASM. And d2j-smali is a bak/smali disassembler.