Tools
MultiMC has built-in support for a few Minecraft and Java-related tools. If you'd like another tool added then create a feature request.
To set up the tools, you need to first download it to a location you can access and then click on this button --> 
To run a tool, either right click the instance, click Play and then select the tool, or hold the Play button in the instance toolbar clicked for a few seconds until the same menu pops up. Some tools, like profilers, will launch the game, while others won't.
JProfiler's intuitive UI helps you resolve performance bottlenecks, pin down memory leaks and understand threading issues.
After clicking JProfiler in the Play menu a JProfiler server will be started up at port 42042. You then need to manually start JProfiler and you should be able to connect to the local server, setup everything, and then click Launch in the dialog that MultiMC opens.
Java VisualVM is an intuitive graphical user interface that provides detailed information about Java technology-based applications (Java applications) while they are running on a given Java Virtual Machine (JVM*). The name Java VisualVM comes from the fact that Java VisualVM provides information about the JVM software visually. Java VisualVM combines several monitoring, troubleshooting, and profiling utilities into a single tool. For example, most of the functionality offered by the standalone tools jmap, jinfo, jstat and jstack have been integrated into Java VisualVM. Other functionalities, such as some of those offered by the JConsole tool, can be added as optional plug-ins.
After clicking JVisualVM in the Play menu JVisualVM will be launched. Take your time to set it up, the launch of Minecraft will be delayed until you click Launch in the dialogue that MultiMC opens.
To get you started, go to the Sampler tab and select CPU. Then click Launch in the MultiMC dialogue.
MCEdit is an open source world editor for the popular game Minecraft. MCEdit was first created to allow players to preserve anything built with several old versions of Minecraft and take them forward into newer versions of the game. It also aims to be forward-compatible with future (or even modified) versions of Minecraft. It has since been improved with brush tools for laying down blocks in different shapes, integration with the Minecraft Server to generate terrain using Minecraft’s own seed algorithms, support for multiplayer worlds, and editors for certain blocks including chests and mob spawners.
Get MCEdit here
After clicking MCEdit in the Play menu you will be prompted for which world to open. After doing that you will be launched straight into that world in MCEdit. You can use both MCEdit 1 & 2.