From ModMyiFone - Wiki
Installer.app is now called apptapp! Mac users now enjoy a full GUI, no-command-line iPhone install process.
Introduction
The apptapp (aka Installer.app) from Nullriver Software is the best and easiest way to install, update and uninstall 3rd party applications on your iPhone. It automatically checks community repositories for updates and new Games, Productivity tools, System Enhancements and Utilities. It could be one of most important contributions towards fueling the iPhone native application movement.
If you're looking to install NES, LightsOut, other games and tools, this really is the easiest, most productive method.
However, Nullriver does not provide any installation instructions, even though it's the perfect tool for people interested in native applications. The process is detailed below for Mac users. Windows users should be able to adapt the instructions for their system easily.
Another important note about Nullriver: iPhone Installer is in beta at the moment and Nullriver is known for releasing shareware software. For example, they released a Sony PSP manager that allows you manage and sync your media and settings from your Mac to your PSP. It's certainly possible that in the near future, when Nullriver as a company, feels comfortable with the idea of selling a native iPhone application, they could start charging for Installer. Obviously, a lot of work is going into this tool, and if it continues to be refined, some may think it's worth a shareware fee. You are warned that it may not always be free, but let's hope the beta lasts a long time. Perhaps iPhone native app development will continue to be considered a fringe activity until officially sanctioned by Apple.
Consider referring to the guide I wrote on my own site for more information and related frequently asked questions to supplement what's offered here.
See my iPhone Mod Guide
Update
Nullriver has made installing their Installer, apptapp, even easier, by offering a single-command script that handles everything required in a single step. Check out their site for download. They recommend that this method be executed on a freshly restored iPhone, so it may not work for everyone. Otherwise, follow the steps below to manually install on a previously modded system.
Preparation
1. Unlock iPhone with jailbreak. Use either iActivator or do it on the command-line in Terminal.
See:
Getting_Started_iPhone_Modding
Windows_iPhone_modding_101
Jailbreak_iPhone
2. Install iPHUC. Follow the instructions posted on this wiki. Unfortunately, this is still an arduous process involving the installation of various code tools and libraries. Luckily, the process is well documented and you only have to do it once.
See: Installing_iPHUC_iPhone
3. Install SSH. Follow the instructions posted on this wiki. Luckily, once you get Nullriver's Installer installed, you can upgrade to OpenSSH and maintain it more easily.
See: Installing_ssh_on_iPhone_using_iPHUC_in_OS_X
Manually Install Installer.app
1. Download Installer.app ZIP file from Nullriver, unzip, and move into your local “phonedmg” folder with your usual drag-and-drop interactions. Make this folder, if necessary: ~/phonedmg/Applications/
2. Shut down iTunes, and use Activity Monitor to quit iTunesHelper. (see iActivator guide for details, it should be familiar from step #2 above)
Getting_Started_iPhone_Modding
3. Open iActivator, and do a Jailbreak, or use your preferred method.
4. Open Terminal on your Mac.
5. Find your iPhone’s IP address: iPhone > Settings > WiFi > blue-arrow on current network > 10.0.1.4 (sample address)
We’ll use the IP address 10.0.1.4 in this guide. Your IP will probably vary, so remember to replace it with yours each time you see in the code examples.
6. Type (replacing with your iPhone’s IP address)
ssh -l root 10.0.1.4
7. When prompted, enter default password (unless you’ve already changed it)
dottie
8. Now you'll create the application directory on your iPhone. Type (hitting return after each line):
cd /Applications
mkdir Installer.app
exit
9. Now you're back in the Terminal accessing your local machine. Type:
cd ~/phonedmg/Applications/Installer.app
10. Now you'll copy the Installer.app you downloaded from Nullriver to your phone with secure copy. Type: (replacing your IP address)
scp * root@10.0.1.4:/Applications/Installer.app
[password "dottie"]
11. Now you'll enable the Nullriver Installer with permissions to run. Type: (replacing with your IP address)
ssh -l root 10.0.1.4
[password "dottie"]
cd /Applications/Installer.app
chmod +x Installer
chmod +x ditto
exit
12. Hold down Sleep button and slide power off. Restart iPhone
13. The Installer widget icon should appear in the Springboard. Use it to install the available packages, especially, Mobile Launcher, BSD Subsystem and Open SSH. You’ll probably find dozens of interesting native applications to try, all of them constantly being updated and easily maintained with Installer.
14. You’ll always need to be jailbroken to allow the apptapp Installer to write to the iPhone file system. Keep this in mind if you get any installation errors when using Installer.