I think I have written that before, but the following is a short general difference in DP world concerning keys (not sounds!).
All major companies have at least 2 types of keys: "light" and "normal"
Even when not specified, it is pretty easy to check what is used: everything with stage weight under 17kg has "light" version, 17-20kg is not clear, 20kg+ have "normal" keys. Note that specification is really about the weight of the key construction and not about how hard you should press the keys, all of them are "imitating" pianos and pianos have a "standard" defining the weight which trigger the key (unlike synth actions, which have no such standard). The "lightness" comes for price, light keys are playable but the feeling is different (think of cheap vs expensive encoders or faders, even with the same force needed to operate). Also some cheap light keys (for example from Yamaha) are technologically synth keys with extra "hammer" attached (without pivot point imitation and other cuts).
Kawai has RM and Grand feel actions. These are physically imitating piano keys, including the length. Also the mechanic is located at the end of the key (like in real piano), unlike all other types where it is located under the key. That also means the dust and dirt which is unavoidable comes between keys does not affect the thing. Other companies do not have equivalents for these actions (well, Yamaha had Nu...)
There are actions about which there are many speculations, so called "wooden" actions. Constructively they are the same as "normal", but wood is integrated into the key. While you never really touch it (all keys have plastic "Ivory" on top), that can add some stability and weight. Still, the length of the key is not real as well as the mechanic.
The list of producers which have own actions: Yamaha, Roland, Korg and Kawai (not sure about Casio and Akai). Hammer actions from other companies normally have some version of Fatar OEM inside.