Windows only: Portable application NirLauncher bundles 100+ of the best NirSoft utilities into a single launcher window, and even allows you to add your own utilities to make a killer flash drive toolkit.
Once you've downloaded the zip file, you can extract the contents into a new folder on your desktop or flash drive, and then launch the NirLauncher.exe application from that folder, which will give you quick access to the 100+ NirSoft utilities included in the package.
It's important to note that because of the system-tweaking, hacking nature of the NirSoft utilities, they sometimes come through as a false positive on your anti-malware utility — but that doesn't mean that they are infected with a virus. Depending on the type of system protection that you have installed, you might have to remove the files from the quarantine folder in order to use all of the utilities.
Tweaking the Launcher
You can edit the included NirSoft.nlp file in a text editor to add or remove the utilities that you prefer — or you can even create a new .NLP file with your own customised settings. Just make sure to use relative paths to the executable files to make sure that they will be portable when you put it onto your flash drive.
The NirSoft blog even provides a launcher file for the suite of awesome, portable, system-tweaking tools from SysInternals — simply download the launcher file and extract all of the SysInternals applications into a folder, and then use the Launcher -> Add Software Package menu to add the entire group into the application. Once you've got them there, you can switch between the NirSoft and SysInternals groups with the F3 key, or through the Launcher menu.
NirLauncher is a free download for Windows only. What applications would you include in your own portable flash drive toolkit? Tell us in the comments.