Adding simple & free effects

From time to time, pictures taken are too dark, too light, or just need some emphasis or added vibrance.
I love the free app called photoshop express, allowing me to add a number of basic effects at the tap of my screen. So simple! Below are examples of such. I particularly like the vibrant effect (which can really bring some pictures to life, enhancing existing colour tones), exposure effect (lightens dark photos), and vignette blur (places emphasis on a focal point within the picture whilst blurring the background "noise").

Modern cloth nappies: vibrant effect, vignette blur effect
Little gum tree- vibrant effect
Reedy wetlands- exposure effect
Home grown corn- vibrant effect