VLC Player too has an inbuilt converter.
JDownloader 2 (link with official adfree version provided by the dev) : This can download any video from most videohosts. As well as direct video links.
Youtube & Videos
Video Download Helper Works with Popular browsers for downloading youtube videos.
IOS: Cloud Video Player
Note: Downthemall does not work with the new firefox quantum. (FF version 57). Use Waterfox instead.
IOS: This version of Repost Saves Stories, Videos and Images. Bit of a warning, it’s loaded with too many Ads and Ad spots.
Android: Story Saver
Gif and Video Editing.
gfycat and imgur have their own inbuilt tools. However for more intricate editing.
Professional:Sony Vegas (easy), Premier Pro.