ET
Well these are a very good start for pretty much any mocker, no matter what era you're trying to replicate
GIMP: http://www.gimp.org/
Audacity: http://audacity.sourceforge.net/
Blender: http://www.blender.org/
Inkscape: https://inkscape.org/en/
Paint.net: http://www.getpaint.net/
Synfig: http://www.synfig.org/cms/
Some of the best mocks on the internet have been done with open source software, take a look at Dave Jeffrey for example https://www.youtube.com/user/stupidrubbish
Although theoretically you could come up with a masterpiece even when relying completely on Paint, Powerpoint and Movie Maker if you really knew what you were doing.
Not that using the software I listed will instantly make you a genius however, you'll probably have to take some time to get to grips with your chosen tools. I believe this involved GIMP to some capacity
GIMP: http://www.gimp.org/
Audacity: http://audacity.sourceforge.net/
Blender: http://www.blender.org/
Inkscape: https://inkscape.org/en/
Paint.net: http://www.getpaint.net/
Synfig: http://www.synfig.org/cms/
Some of the best mocks on the internet have been done with open source software, take a look at Dave Jeffrey for example https://www.youtube.com/user/stupidrubbish
Although theoretically you could come up with a masterpiece even when relying completely on Paint, Powerpoint and Movie Maker if you really knew what you were doing.
Not that using the software I listed will instantly make you a genius however, you'll probably have to take some time to get to grips with your chosen tools. I believe this involved GIMP to some capacity