Android: When you need to quickly start any app, Slide Launcher can be your best friend. It's fast, it's pretty and it's really light on the resources, claiming no RAM and battery usage while running in the background.
To activate Slide Launcher, you need to slide upwards from the Home button. The launcher is a pattern of circles called "targets" with one-tap access to apps, contacts (cards, direct calls or direct messages) and system actions, which you can set up. It's very customisable, letting you choose the layout, the space between targets, background settings, icon themes, tooltips, frames, haptic feedback, floating window (where supported) and cache. It's similar to SwipePad, but way lighter on your system resources.
The only hindrance right now is that it requires a phone that has a virtual home button, which means Samsung handsets are out of the question. But the developer suggests that you use a third-party app like Swipe Home Button and set it to start Slide Launcher with the same action. I tried it out and it works flawlessly, so give it a go.