Snapseed is a completely free editing app and is like the free version of photoshop for your photos. Maybe you want to get rid of an object or blur a part of your photo. Snapseed works well for professional photographers looking for an easy program to make quick/small edits but they may find that Lightroom is much less restrictive in terms of colour editing tools.
2) ADOBE LIGHTROOM
Another free app where you can use presets to edit your photos to your perfect aesthetic theme to your Instagram posts. You can adjust the temperature, white balance, saturation, and exposure as well as individual colours. This is the best app to edit the colours in your photos.
You also have much more control over light levels as well. You can easily raise midtones, highlights or shadows as well as with specific colour channels.
This can be a life saver when using props, for instance let's say you're using a cup as a prop but when you go to edit your photo is quite obviously empty... you can easily add that joe in by sketching inside that cup.
It can also make things shine more, ie accessories or your eyes if the lighting has made them a little yellow. You can use whiten on the background to give it a super cool tone as well if you're going for that white aesthetic.
It is a useful tool for makeup artists too who might not have the professional lighting required to show off their skills appropriately (highlight and eyeshadow just doesn't look as bright on camera as in person).
It's easy to keep editing and editing because of insecurities however so please read this VOX article about overediting.
While this isn't necessarily an editing app, UNUM does help massively in planning your instagram feed so that it makes sense and is aesthetically pleasing. This is especially helpful at planning out sponsorships or other content so that they are best spread out.