Intellij - Since we are mostly developing Java related stuff, mostly stick with Intellij platform. It's easy to use and almost all the things that need for Java development is there.
Google Drive/Gmail/Hangout - Google Drive to create Docs/Presentations/Sheets since developers can work and design collaboratively. Hangout and Gmail used as messaging platform.
VIM - This is the best developer friendly text editor that I h'v used so far. Since we are working with jar/zip files mostly, Sometimes we need to change a file inside this zip files. Using VIM editor, we can change its content without even unzipping files.
Docker - In some instances, we need to install databases / load balancers / servers etc only for the testing purposes. Some of these software are really hard to install since the software has third party dependencies. Docker keep life simple by simply pulling the appropriate image into the local computer and running it with a single command. I used Docker images especially to install databases like Oracle, MySQL since I don't need to install those software on my computer. I can simply kill the container once I've finished using the application.