Rigi Picker is a bone-selection add-on from Bookyakuno that works alongside Rigify and its rig picker to make posing easier. It lets you select IK, FK, and Tweak bones for the arms, legs, torso, and fingers. Smooth selection tools let you add to a selection with Shift and remove from it with Alt, while a dedicated button switches bones between FK and IK. You can also show only the bones of the currently displayed layer.
A user bone picker lets you add bones of your choice as picker buttons, and it works with bones outside Rigify as well. The Rigify Basic Human and Human meta-rigs have full support, and other rigs can work if their bones share the same names as the Human rig's bones. The Rigify features target Rigify version 0.6.1 and later, which comes with Blender 2.83 or newer.
Rigi Picker is reached from the 3D View sidebar, with a pie menu on W and a popup menu on Ctrl+W, shown in pose mode and bone edit mode. Documentation is available, and the add-on is distributed under the GPL license.