Excellent question and I will list the tools I have tried and report back the results -- the listing here is more in a chronological order and doesn't represent a "ranking". In most cases, a ASCOM connection between the laptop & mount is needed and many tools also will use a ASCOM camera driver (NOTE : if you have a SLR, you do not have a ASCOM-compatible camera)

It is a work in progress -- I'll update the different sections as I have time to try the tools. The trouble I am having is the tools I have tried give me contradicting results. That's something I have to resolve first.


ASTROTORTILLA + APT (13EUR)
Astrotortilla's main duty is "plate solving" and I use it to confirm or correct slews to a target. It can control ASCOM cameras directly and also supports a separate image acquisition tool (APT) to use dSLRs as well as a ASCOM camera.
Seamless workflow from image capture with my (Canon) SLR, through solving & slew to the intended position made this my first choice. For polar alignment, I leave the mount in HOME position, switch off tracking and repeatedly solve the position as I make mechanical adjustments. AT will process the image and you should watch the solved position : It will show RA/DEC and with some practice and good preparation, it doesn't take long to point the mount 1/2°...1/5° from the NCP. Reading DEC you see the amount of the error, RA gives you the direction.
During preparations, I make sure the tripod is leveled -- usually within < 0.2° error.
PS : APT does more than "just" polar alignment and the 13EUR is a good deal for a useful tool. AstroTortilla is open-source & freeware


APT's built-in DARV (CCDalign) algorithm
The main concept here is to let the mount slowly slew at sidereal speed in one direction and later slew the same amount into the opposite direction. When your mount is accurately aligned, the startrails fully overlap. Otherwise you see a "V" and the width of that opening is an indication of the misalignment. You make mechanical adjustments and repeat the step. Once done, you have to do the same for the other axis and alignment star.
IMO that is a very elegant solution, taking advantage of the long exposure capabilities of the camera and delivers an easy to read indicator for the size of the error. It still requires more knowledge & interaction from the user as he/she has to select suitable alignment stars and slew the mount into position.


ALIGNMASTER (14EUR)
Unlike the other tools, Alignmaster doesn't require an imaging camera -- good news for visual observers. Of course, you can use the camera's rear LCD & Lifeview or stream the view to another app on your laptop.
The list of acceptable alignment stars is short -- but you can extend it (edit a text file). Based on date, time & location, the program will recommend pairs of alignment stars -- it doesn't take visual obstructions into consideration. That's your job. The procedure itself is simple : The tools slews the mount to a star's supposed position and you make the adjustments until the star actually is inside the crosshair. After that, AlignMaster will calculate the Altitude & Azimuth errors and slews the star off center. Turning the mechanical screws, you adjust the mount till the star again is in the crosshair.
You should repeat that until the errors are low enough.

AlignMaster's alignment sequence is very similar to the 2-star alignments modern GOTO mounts do. The mounts usually don't offer a easy choice of alignment star pairs (limited display).


PHD & PHD2
Many people use these tools for autoguiding -- the functions to help you with DRIFT ALIGNMENT are often overlooked. PHD2 has made that task more user-friendly. I think it will work similar to DARV / CCDalign in that you temporarily disable tracking and observe the deviation (and correct that).


WCS WebCamScheinern (21EUR)
This too is a tool targeted at a different group of cameras : (modified) streaming WEBCAMs. Recently they've added support for the models from ImagingSource (e.g. the popular DMK series)


EQALIGN
This _ONLY_ works with ASCOM cameras -- not with dSLRs. I'll try EQalign out later but would like a solution that works with both cameras.


BACKYARDEOS V3 ($50)
It's been a while since I used that -- it has an adjustable reticle to track the drift. I am not sure what further improvements the current version has. When I compared BYE to APT, APT won me over with the good integration of ASCOM + Canon camera support and AstroTortilla interface.


ASTROPLANNER
This too can use your time & location to determine suitable pairs of alignment stars. It also can communicate with ASCOM mounts, but I am having trouble with that setup. Especially when I include a ASCOM hub. Also, Astroplanner inquires various ASCOM features but some drivers have trouble with that. some mounts don't accept SYNC commands and Astroplanner uses those during alignment.


Sequencegenerator PRO ($100)
It can use PINPOINT ($150) & ELBRUS ($0) plate solvers and at least can accurately point at Polaris. Just as with APT. SGP supports dSLRs. Even some NIKON models !!


OTHER TOOLS
This list is by no means complete -- some tools are free but they rely in expensive infrastructure ("The Sky" "Maxim DL"). If I decide to make that leap, I'll try out those as well.


MY EXPERIENCE with these tools :
APT + AstroTortilla work really well together, both with ASCOM CCD and (Canon only) dSLR. After several comparisons with other tools & during the tests of polar alignment, I am not sure anymore about the accuracy of the reported position. And if the reported position isn't accurate, the polar alignment suffers too.

AlignMaster has a good reputation and the tool calculated errors much bigger than the error I was expecting ==> Now I am investigating what goes wrong and what result I can trust.

Maybe the only way to settle this is a god-old-fashion drift alignment -- but there are additional mechanical problems that can be involved. The mechanical setup of the mount's base now appears to be accurately leveled, I suspect there is some noticeable CONE ERROR and that can mess up the alignment.

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LINKS :
www.ideiki.com
sourceforge.net/projects/astrotortilla
www.alignmaster.de
www.stark-labs.com/phdguiding.html
openphdguiding.org/
http://wcs.ruthner.at/index-en.php
eqalign.sourceforge.net
www.backyardeos.com
astroplanner.net
www.mainsequencesoftware.com
www.astrosurf.com/pulgar/elbrus/elbrusin.htm

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