Randomize Sectors form: floor/ceiling height controls now have "Offset mode" drop-downs. Available modes are "Raise and lower" (default), "Raise only" and "Lower only".
Consistency, Randomize Sectors form: persistent settings are now saved only when applying changes done in the form (e.g. in the same conditions as in Randomize Things / Vertices forms). 

Fixed: Randomize Sectors, UDMF: vertex height changes were not undone properly after using the mode (I broke it in r2101).
Fixed: Randomize Sectors: floor/ceiling textures can not be used as lower/upper textures when "MixTexturesAndFlats" is disabled. In this case the corresponding option is now changed to "Use default texture".

Randomize Sectors form: added "Use vertex heights" check-boxes. When enabled and used on triangular sectors, it can be used to create a terrain-like look.
Updated ZDoom_DECORATE.cfg.
Updated documentation, rearranged contents a bit.

Fixed, WavefrontExporter: floor and ceiling textures were not exported when using "classic" game configurations (ones with disabled "MixTexturesAndFlats" option). This should also fix incorrect flats on exported model when there are flats and textures with the same name.
Fixed, WavefrontExporter: 3d floors geometry and wall geometry around them was created incorrectly.
Fixed, WavefrontExporter: floor and ceiling textures of non-Vavoom 3d floors were swapped on exported geometry.

Fixed incorrect non-UDMF <-> UDMF skills translations in Strife_misc.cfg.

Renamed "Save Screenshot (editing area only)" action to "Save Screenshot (active window)". It will now save a screenshot of currently active window, or editing area if no windows are open.
Added icons for "Save Screenshot" menu items.
Development: "Save Screenshot (active window)" action will work on a child Form only if it is inherited from DelayedForm.

General interface: dynamic lights rendering mode and model rendering mode are now selected via drop-downs.
Renamed "Toggle dynamic lights rendering" action to "Show dynamic lights".
Changed: "Show dynamic lights" action now toggles between available dynamic light rendering modes.
Renamed "Toggle models rendering" action to "Show models".
Changed: "Show models" action now toggles between available model rendering modes.
Removed "Toggle dynamic lights animation" and "Render selected/all models" actions.
Fixed, Randomize Sectors form: selection highlight was not updated after applying the changes when the form was shown in Sectors mode.
Consistency: selection is now cleared after applying changes done in Randomize Things and Randomize Vertices forms.
Fixed, Classic modes: sprites of things with attached models were not rendered when model rendering was disabled.
Updated documentation.

Changed FormBorderStyle from FixedToolWindow to FixedDialog. GZDB should no longer disappear from the alt-tab list when a child form is opened.

Visual mode: "Lower/Raise Floor/Ceiling" actions now work on surfaces with sector slopes.
Cosmetic: numeric textboxes, which support relative values, now have differently colored text and a tooltip.
Internal: renamed Sector.CeilingSlopeOffset to Sector.CeilSlopeOffset, Sector.CeilingSlope to Sector.CeilSlope to match their names with similar sector properties.

Internal: added General.Interface.ActiveDockerTabName property.

Fixed: VirtualSectorField was cleared from sector properties when pasting map geometry in Doom/Hexen map formats leading to incorrect sector assignment [I broke this in r2009, so it seems].

Fixed, Classic modes: Alt-dragging map elements (e.g. "snap to grid increment while dragging" mode) was not working properly.

Map Analysis, internal: some ErrorCheckers and ErrorResult had inconsistent namespaces.
Thing Edit forms, internal: optimized missing flags check a bit.

Thing Edit Form: a warning is now displayed when a thing doesn't have any skill or class or game mode flags.
Game Configurations: moved "thingflagscompare" from Game to Map format blocks. "Check stuck things" check now works properly in Doom/Boom game configurations.
Map Analysis: fixed a possible crash during "Check texture alignment" check.
Map Analysis: ResultStuckThingInLine now highlights both thing and line.
Map Analysis: ResultStuckThingInThing now highlights both things and allows to delete any of them.
Internal, Map Analysis: rewritten parts of "Check stuck things" class.
Internal, Map Analysis: changed the way processed stuff is stored in "Check texture alignment" class.
Internal: changed CurrentDomainOnUnhandledException, so ExceptionDialog with proper info shows up even if adding exception to the Event Log failed.
Internal: changed format, in which thingflagscompare info is stored.

Fixed incorrect syntax in ZDoom_DECORATE.cfg.

Map Analysis form: fixed a crash caused by running analysis, opening another map then trying to run analysis again.
Map Analysis form: error checks are now alphabetically sorted.
Map Analysis form: added "Toggle All" check box.
Internal: CheckboxArrayControl now has Sort() method.
More fixes in ZDoom_DECORATE.cfg

Added: Map Analysis: added "Check texture alignment" check. Currently it works only in Doom/Hexen map formats.

Fixed: Drag Geometry Mode: dragged sectors, linedefs or vertices were snapped to 0, 0 in some cases when trying to snap them to a linedef fully inside of a grid cell.

Fixed: Visual mode: "Select" action with "with the same textures" / "with the same height" modifiers (Shift/Ctrl + LMB) was not working properly when used on vavoom-type 3d floor sidedefs.
Fixed: Visual mode, UDMF, "Auto-align textures" actions: vertical texture offset was calculated incorrectly for vavoom-type 3d floors.

Visual mode: "Select" action with "with the same textures" / "with the same height" modifiers (Shift/Ctrl + LMB) now works properly with vavoom-type 3d floors.

Visual mode: "Select" action with "with the same textures" / "with the same height" modifiers (Shift/Ctrl + LMB) now works when used on floors and ceilings of a 3d floor.

Sector slopes were not copied by "Copy Properties" actions and were missing from Paste Properties Options form.
Added several missing flags to ZDoom_DECORATE.cfg.

Visual mode: "Select" action with "with the same textures" / "with the same height" modifiers (Shift/Ctrl + LMB) now works when used on sides of a 3d floor.
Visual mode: "Select" action with "with the same textures" modifier (Shift + LMB) now selects adjacent sidedefs only when their height intersects with the height of the current sidedef.
Visual mode: "Select" action with "with the same textures" modifier (Shift + LMB) was not selecting connected one-sided sidedefs when used on a sidedef without a texture.
Cosmetic: fixed a couple of action descriptions in BuilderModes' Actions.cfg.
Cosmetic: MainForm.UpdateToolStripSeparators was working incorrectly in some cases.
Cosmetic: ErrorChecksForm's title was not updated when no errors were found.

The editor will fail more gracefully when no D3D device is detected.
In some cases the editor was constantly checking D3D device availability when minimized.
Added more DX-related debug output (only in Debug builds). 

Preferences: added "Vertex scale (3D)" preference, renamed "Vertex scale factor" to "Vertex scale (2D)".

Map Analysis mode: fixed a couple of minor glitches related to enabling/disabling results list, "fix" buttons and "fix all" checkbox.

Updated documentation.

Map Analysis mode: results list now has a context menu, which allows to hide/show results based on type of selected result and to  copy description of selected result to clipboard.

Map Analysis mode: export to file command will now show "Save File" dialog instead of putting the file in the same folder as the map, also added some boilerplate.
Tag Explorer plugin: save to file command will now show "Save File" dialog instead of putting the file in the same folder as the map, also added some boilerplate.
Internal: reformatted GZCrash.log a bit.

Comments Panel: probably fixed a possible crash when UpdateList() is triggered during map unloading.

Map Options Form: example map name now uses current game's naming scheme.

Texture Browser Form: some minor logic fixes (no texture groups were selected when initial texture was empty and no texture group was stored in the program configuration).
Texture Browser Form: don't save current texture group when the form was canceled.
Keyboard Shortcut Reference export: generated html will now be saved to program configuration folder if working folder is write-protected.
Internal: added SupportedMapFormats property to EditModeAttribute. A mode with this property specified will be available only in specified map formats.
Interface: Ceiling Align Mode and Floor Align Mode are now enabled by default.
Interface: Ceiling Align Mode and Floor Align Mode are now only available in UDMF map format.
Interface: Visplane Explorer Mode is now available only in Doom map format.

Find & Replace Mode: sector effects and linedef actions are now searched on bit by bit basis. That means map elements with partially matching Generalized effect/action can now be found.

Internal, Edit Sectors form: more changes to "Slopes" tab logic. It's still incomplete...

Import .obj as Terrain: created terrain was horizontally flipped when importing a model with up axis set to X or Z.
Also, I would like to use this opportunity to thank Siberian Tiger from DTD Team for helping me with SVN builds for more than two years. You made my constant wrestling with the code a much less tedious process.