I've been using PostBuilder (used to be called gramspacer) for several months now and I use it almost every single work day. PostBuilder makes it super convenient for organizing and planning content for my Instagram pages and the founder is very responsive if you have questions or if there's ever an issue. I definitely recommend them!
Magisto - Magisto online video editor is a fast & powerful video maker. Turn your photos and video clips into video stories with Magisto movie editor. Start free!
Instaspacer - Putting the spaces back into Instagram
Kudoflix - A new video editor made for all. The only movie maker that gives Professional results without spending time or money learning or rendering.
PicMerger - Merge photos side by side, create beautiful photo collages, customize your content with built-in photo editing tools, and more
Kizoa - Kizoa is an Online Movies and Videomaker application that use photos, videos and music to design and stunning stuff.
StoriesStudio App - StoriesStudio allows you to take a long video and cut it down into separate clips that can then be uploaded to Instagram stories, WhatsApp, TikTok, and more.