A few applications that support the FreeFrame plugin standard, with links to more info about their FreeFrame support:

Modul8 (info from forum)

Isadora (FreeFrames in Isadora)

Salvation & SalvationMX

VJamm3

VDMX5

FrameRunner (Aftereffects Native Plugin/Host for using FreeFrame plugins inside Adobe AfterEffects)

VVVV (about FreeFrame support in VVVV)

FFRend FreeFrame Renderer (homepage)

Eyesweb (external info on FreeFrame support)

Livid Instruments Union & Cell DNA  (news on their FreeFrame support as of 2008)

Neuromixer AVMixer Pro & AVPlayer Touch (about FreeFrame support in AVMixer Pro)

Other apps: some more information can be found @ freeframe.sourceforge.net and community.freeframe.org.