Air Manager, by Sim Innovations, is a very sophisticated panel and instrument development tool. You can create some very detailed instruments with it that can closely replicate the look and feel of the real instrument. There are a number of preconfigured panels and instruments but if something you need is missing the effort to create one is involved. Air Manager is also considerably more expensive than X-KeyPad.
X-KeyPad Virtual Devices are simpler in that they can only be configured as a keyboard grid layout. This allows you to pack a great deal of functionality onto one panel. Configuring X-KeyPad is similar to Air Manager in that you do need to understand the commands and datarefs associated with the aircraft’s function you are trying to control but you usually can configure the key in X-KeyPad without the need for Lua programming.
