Obviously this list would change depending on what is available in the market place but as of now this is my take on what is available and how they operate: Wacom - the prime active digitizer that can also have an additional touch layer added to the top of the screen to provide multitouch and pen input at the same time. There is no battery in the pen as the powered sensor grid is located below or under the LCD in the device. N-trig - this is a dual screen input system as well (pen and touch) with the pen containing a battery and the sensor grid in the device which is not powered. The system is presently at v3.5 (or maybe 4) and is contained only in the Sony devices at this time but just went out of production on the Fujitsu Stylistic slates. Atmel - the first of the 'active capacitive' digitizers where a powered pen called a 'MaxStylus' interfaces with the touch sensor to provide pen input. Atmel is actually pretty big in the touch screen sensor panels in cell phones and phablets. Most of the devices where touch input is considered to be very 'smooth' they have Atmel sensors. Version 1 of the new optional stylus input was in the Motorola XOOM and the stylus used a AAAA battery. Version 2 was in the HP Elitepad 900 and used a AAA battery. The new version 3 is in the HP Elitepad 1000, Professional Tablet 610, and Elitebook 810. Synaptics - a newcomer on the market for touch panels and pen input. The system is similar to Atmel and called an 'active capacitive' system. This is presently at version 1 and is available in the Dell Venue Pro 8 and Pro 11. The pen uses a AAAA battery. Now for my take on the operation: Scale for the following is 1-10 (I know, not very computer of me but I don't want to call anything a zero...it is just a subjective scale) where 1 is terrible and 10 is beautiful. Also, the observations are based on my Fujitsu T731 (Wacom), HP 2730P (Wacom), Fujitsu Q550 (N-trig v3), Fujitsu Q702 (N-trig v3.5), Dell Venue 8 Pro (Synaptics v1), HP Elitepad 900 (Atmel v2), and HP Elitepad 1000 (Atmel v3): Wacom - 8 - The Good - the pressure capabilities for art, no battery in the pen, good overall performance, nothing to go wrong in the pen as far as corrosion or connection issues (read below); The Bad - screen graininess, digitizer is located under the LCD giving a degree of 'depth' when you use it, inacuracies on the edges and in the corners, transition between touch and pen is not smooth and is the subject of most of the criticisms of 'laggy' performance. Atmel v3 - 8 - The Good - pressure works great for note taking and sketching and may actually work well enough for art use too but we will not know until someone tries it, good overall performance, inking is smooth and looks good, screen looks outstanding, accuracy is good everywhere on the screen, transition between touch and pen is smooth and has no perceived lag; The Bad - battery in the pen but it is at least a AAA size, Atmel v2 pens had long term issues with internal corrosion (the durability of the v3 pen is TBD but there were significant internal changes). N-trig v3.5 - 7 - The Good - pressure works but has been rejected for art use, good overall performance but the inking lines are smaller than Wacom and/or Atmel v3, durability has been proven to be much improved over N-trig v2, long battery life in the pen, screen looks good, accuracy is good at the edges and in the corners; The Bad - AAAA battery in the pen (expensive and not on every battery tree at the corner store), tapping noise is louder than Atmel v3 or Wacom, transition between touch and pen is not smooth and is the subject of most of the criticisms of 'laggy' performance. Synaptics v1 (based on my A01 Feb 2014 pen on my Venue 8 Pro) - 5 - The Good - pressure works for note taking and sketching but is likely to not be good for art work due to inking variabilities and other inking issues, not as good overall performance due to wide variabilities in reported quality, inking lines are heavier than Wacom and/or Atmel v3, screen looks great, accuracy is good at the edges and in the corners, transition between touch and pen is smooth and has no perceived lag; The Bad - AAAA battery in the pen (expensive and not on every battery tree at the corner store), connection issues inside require constant fiddling to keep the pen workng. As a proof of concept this system may be good with a new pen design but a better pen is not yet available [Note: A02 March 2014 build pens are reported to be arriving now but the performance appears to be inferior to the A01 February 2014 pen]. Atmel v2 - 3 - The Good - works for limited inking and makes a good mouse replacement while mobile, screen looks great, transition between touch and pen is smooth and has no perceived lag; The Bad - inking variability and corrosion issues inside the pen make this not recommended for anything other than basic note taking. Two additional observations; if Synaptics makes as much of a stride with an eventual v2 when it comes out as Atmel made from v2 to v3 then it will be a great alternative. Also, if the long term durability and battery life of the Atmel v3 is as good as the N-trig v3.5 then this system may move to a '9'! Am I kidding? No, I am not! The only unknown about the Atmel v3 so far is the art use performance potential. Once that moves into the light we should see a new bunch of reviews. Enjoy!