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 a versatile map utility, designed for editing Minecraft maps. With it, you can open a level and fly around in glorious 3D with multiple levels of detail! Select millions of blocks and clone them anywhere else in the level. Fill a boxy selection with the block of your choice, or replace one kind of block with another. Export blocks to a schematic file for later use. Import a schematic or an entire level into any world using import. Move players, spawn points, or even add and delete players. Create and and remove chunks from the world. Fill blackened areas with light. And much more with modular filters!
NOTE: MCEdit is not able to open worlds for versions newer than Minecraft 1.13
Get MCEdit Unified here
After clicking MCEdit in the Play menu you will be prompted for which world to open, then you will be launched straight into that world in MCEdit.