Special References

2010/06/21:
entry updated (-> AutoCAD's Commands Reference (at cadmaro.de))
**

AutoCAD Commands and System Variables:

The AutoCAD user's help file of course has lists of the commands and the system variables (sorted alphabetically). However, these are only for the current AutoCAD version. Here are some more listings which also take older versions into account:

AutoCAD Commands (at hyperpics.com)
for all AutoCAD versions from release 2000 upward in comparison

AutoCAD commands dictionary (at cadforum.cz)
for all AutoCAD versions starting from release R12 upward. It shows the version when the commands where introduced. Typing into the input-field immediately shows all matching commands. It also comes in a couple of local language-versions (i.e.: German, French, Spanish, Italian, Portuguese).

AutoCAD's Commands Reference (at cadmaro.de)
for AutoCAD versions from release 2002 upward in comparison (to the most recent previous release) with command options 
Attention: Although the linked site is primarily in German, it compares the German and English command's counterparts side by side. This means that all the commands are visible in English too - you just have to look closely. On the top of the page you can select the AutoCAD version. In the table, yellow (red for 2010) means new command, cream means changed command and blue (grey for 2010) means that the command is not supported/available anymore.

AutoCAD's System Variables Reference (at hyperpics.com)
for all AutoCAD versions from release 2000 upward in comparison

AutoCAD system variables (at cadforum.cz)
for all AutoCAD versions starting from release R12 upward. It shows the version when the system variables where introduced. Typing into the input-field immediately shows all matching variables. 

DXF:

AutoCAD's DXF References (at autodesk.com)
for all AutoCAD versions from release 13 upward (The current one is also part of the Developer's Documentation in the help file.)

ActiveX/COM (used i.e. in AutoLISP and VBA):

Acad-AX-History-Methods-Properties (pdf) (xls) (at cadwiesel.de)
for the AutoCAD versions 2000 to 2006 in comparison

AutoLISP Functions References:

There is the "AutoLISP Function Synopsis" in the developer's help file in the chapter "AutoLISP Developer's Guide" / "Appendixes" and especially for the DCL-functions there is the "Programmable Dialog Box Reference" in the chapter "AutoLISP Developer's Guide" / "Working with Programmable Dialog Boxes". For whom ever that is not enough, here are some more:

(Asmi(Tools)) AutoLISP Help (at asmitools.com)
A general AutoLISP functions reference "sorted according to purpose" into 28 categories and with "additional examples" by Aleksandr Smirnov. It also shows at least the documented ActiveX-functions and the DCL-functions.

Visual LISP Function Reference Chart (pdf A4) (pdf A3) (by Dr. June-Hao Hou)
A similar AutoLISP functions reference for AutoCAD 2000/2002/2004, sorted into 50 categories with ActiveX functions and a few important system variables but no DCL functions. (The name of course is misleading - see my AutoLISP-Intro, 5th par. ff. "Secondly...")

Catalog of Function Definitions by Ron Leigh (at ronleigh.info)
Another (older) AutoLISP functions reference sorted into 21 categories. It does not show any ActiveX-functions nor any DCL-functions.

AutoLISP Functions (pdf) (jadp.co.uk)
Yet another (older) AutoLISP functions reference sorted into 32 categories. It also includes the DCL-functions but no ActiveX-functions. The advantage might be, that it is on pdf, so it may be easier to print.

Other AutoLISP Specific References:

OpenDCL (Runtime) Reference (at opendcl.com)
For more on OpenDCL see their Homepage. (This link is also available under the section "AutoLISP: Online-Tutorials".)

ACET Functions Reference (html) (at afralisp.net) or
ACET Functions Reference (zip -> pdf) (at jtbworld.com)
I will write more about the ACET-functions later on under the menu-link "The ACET-functions in more detail". (These links are also available under the section "AutoLISP: Single Articles for Adv. Beginners". And in case the AfraLisp.net site gets display incorrectly in FireFox 3.5 or higher then look here.)

DOSLib Reference (at en.wiki.mcneel.com)
The Reference on their Homepage gives you only a brief overview. For more details you have to download their product and look into the included help file. (This link is also available under the section "AutoLISP: Single Articles for Adv. Beginners".)