Adobe XD lets you create UI/UX designs for a wealth of different screen sizes. It also can be downloaded for free, so you can hone your UI/UX design skills without having to buy a subscription, which can be costly.
Jenkins is easy to scale as demand increases. The declarative pipeline syntax bundled into the project repo is easy to read and maintain. As it's self hosted we don't need to worry about build time limits.
Bitbucket has good integration with Atlassian. Repositories can be organized into projects and the premium features offer controls around pull requests reviews and branch protection
Firebase is the go to solution for a backend environment for any iOS or Android mobile app. It's easy to setup and integrate. As well as containing a wide range of services to meet lots of different needs. The free service tier give you enough headroom to let you experiment and test before committing to the service.
Gradle and particularly the gradle wrapper is easy to use. Bundling all of the information required to build the project along side the source code is a real time saver compared to managing installed versions.
Zeplin is a great piece of software, as it allows us as designers, to send our designs straight to the development teams, and allows them to turn our designs into fully functioning apps. It works seamlessly with Sketch, via a handy plugin.
Slack allows us to communicate with the rest of the Coderus team, as well as external contacts in relation to specific projects. It is simple for us to use and also allows easy and efficient file transfers.
Sketch is one of the industry standards for UI/UX design. The team use it extensively with our key clients to design and refine the flows for mobile app designs.