Download
CHKT for Android, version 1.0.0.
CHKT is not on Google Play yet. Until it is, you install it from here.
The easy way: Obtainium
Obtainium is a free app that installs and updates apps straight from where they are published. Add CHKT to it once and it will tell you whenever there is a new version.
Tap that on the phone you want CHKT on. If Obtainium is not installed, the page it opens explains how to get it.
Or download it directly
One file. Your phone will ask you to confirm, because it did not come from a shop.
Downloading by hand means checking back yourself when there is an update. Obtainium is worth the two minutes for that reason alone.
When it reaches Google Play
The Play version will be signed by Google rather than by us, and Android treats that as a different app. So if you install from here now, moving to the Play version later will mean uninstalling this one first. Export your reminders from Settings before you do, and import them after.