I currently use Swiftly Switch. It is an app that adds a small bar to the side of the device and by swiping that part, I am shown a list of apps of my choosing. This allows me to open apps much faster.
Sadly, it is not open source. Is there something similar but open source?
You mean you need more than being able to launch apps?
If so, then what I use, MIUI's sidebar, is probably not good enough either
Additional settings > Floating windows > Sidebar