Since 3.16 there is also Android port of Tucnak available. Focused on tablets but can be used also on cell phones. Due touch control, not all features must be accessible.

Hardware requirements

ARRL DX contest on Samsung galaxy IIs

Android 5 (API level 21) to Android 14 (API level 34). For older Andorid 4.1 (API level 16), try 4.61.
Only for devices capable running 32 bit apps (armeabi-v7a).
Some new (2024) devices tells about Tucnak incompatibility. AFAIK they expect 64 bit app (arm64-v8a) which is unsupported by Tucnak.
Recommended internet access for DXC/KST

Install

Tucnak is not on Google Play. To install you must allow install of untrusted applications. Then download Tucnak APK package from http://tucnak.nagano.cz/download.php#android and install it manually.

Features not included

Sound recording
FFT spectrum display
Parallel port keying
Bluetooth devices because of no official support for BT from native code
Serial ports - maybe with alternative kernel with proper drivers
Hamlib

Limited support

USB devices (Davac4, Rotar4) - It is compiled but it seems it works only on rooted devices. User must be member of 'usb' group.

Touch control

Start touch on-screen keyboard by click on input line. The behavior of Enter is context-depended. Sometimes send Enter to Tucnak. Sometimes closes keyboard. Comments are welcome.

To send F1 to F10, use FN key, numeric keys will switch to F's.