Tool Box
Since I've seen many projects and therefore worked with lots of different tools, I put together a list of stuff I appreciate.
Unity3D, the cross platform 3D/2D engine for games and apps of my choice.
Git, to not lose any code and make work in teams easy.
Visual Studio, my IDE for C# and JavaScript projects. It's kind of a beast, but has all the functionality you need in one place.
The lightweight alternative to the fully-blown Visual Studio. I use it for many web projects now. It has a lot of plugins for different programming languages. It needs a bit of setup, but has all you need to type some code. Plus it's free.
ReSharper, for faster coding in C# and consistent coding style. The one plugin I use for Visual Studio which makes coding (and refactoring) really fun.
Jira, to work agile in a bigger team. Even works for small teams. It is web-based (a good idea is to host it directly at Altassian to not worry about updates), so no need for an installation on each client. Became much better in matters of response time, so the disadvantage to a desktop client became less and less a problem.
Trello is a lightweight, web-based task management platform. My choice if Jira seems too complicated for the team I am working with, if they already use Trello for other things or if they just don't want to pay for Jira.
Slack is a web-based (clients are also available) team communication tool. It allows text messaging, calls, file transfers. Topics can easily be separated by using channels. I use it most of the time when working with multiple people.
Confluence, a central place for ideas, designs and other documents of a project. You just don't want to mess with Word documents on documentation heavy projects.
Jenkins, because you don't want to deploy your project every day (or more). From a certain team size you'll need regular versions of your project (continuous development). So setting up a build server once to take that work saves you a lot of time. Jenkins is open source, free and well tested.