Wikipedia
VPSKeys
VPSKeys is a freeware input method editor developed and distributed by the Vietnamese Professionals Society (VPS). One of the first input method editors for Vietnamese, it allows users to add accent marks to Vietnamese text on computers running Microsoft Windows. The first version of VPSKeys, supporting Windows 3.1, was released in 1993. The most recent version is 4.3, released in October 2007 .