Termux is an Android terminal emulator and Linux environment app that works directly with no rooting or setup required. A minimal base system is installed automatically - additional packages are available using the APT package manager. Termux combines standard packages with accurate terminal emulation in a beautiful open-source solution. Access API endpoints with curl and use rsync to store backups of your contact list on a remote server.
TJWS is an Open Source HTTP Server and Servlet container written in 100% Java. It's designed to be a light weight, high performing, secure, embeddable, extensible and flexible. Very small footprinted (~100K), CGI, J2EE/JSP compatible. Servlet spec 3.1
S3 Mockup is an Amazon S3 emulator we develop for one of our projects. It can be easy embedded and used in your test framework or running as an independent service. Using this emulator you can easy setup development and QA environment.