Can you expand this question with a bit more detail.
The only plug-in i know of is the FITS Liberator Plug-In for Photoshop and it's also Open Source. There are some Photoshop Scripts, Actions and a Panel for integration with Photoshop at the Download the ESA/ESO/NASA FITS Liberator v3.0.1 | ESA/Hubble | ESA/Hubble page.
As this application is pretty ”old”, it could have some bugs on newer systems.
And the Source Repository: lnielsen/fitsliberator · GitHub
Yes its a fits image file
created in Maxin DL
I have written a plugin called FITSPlug. I have working versions for all versions of PS from v3 to CC x64. I've been using it daily for over a decade and it's endorsed by many high profile imagers, but it is commercial software.
You can read about it on http://Fitsplug.com