To install a non-Market application maybe an .apk file. You needs a tiny tool to browse the SD card and pick the .apk file. This is simply the tool you got free without advertisement and it is very tiny.

Feature
- It is rarely tiny! It takes only 64 KB on your Android phone.
- It supports external SD cards.

P*S: Don't forget to allow the installation of non-market apps in the system settings.