Fear the... REAPER V4

4.0 headline changes:

+ Dockers and toolbars are freely dockable in main window or floatable (up to 16 separate dockers/toolbars)
Drag tabs from a docker to rearrange tabs, create a new docker in another location, or float windows
Create, customize, and freely dock or float toolbars for different uses
+ Envelope editing
Support for copying envelope points with the mouse
Groups of selected points act like contiguous items when moving or copying
Shift+control+drag on envelope segment (customizable) edits the envelope level within the time selection
+ Media Explorer preview time selection
Select a portion of a media file to insert into a project
Optionally loop and/or stretch the selected portion to fit the destination area and tempo
Scroll and zoom the media peaks preview
Control+alt drag the time selection to render a new cropped file to REAPER, the desktop, or a folder
Control+alt drag the time selection to sampler plugins or other applications that support drag/drop
+ Media Item Properties dialog
Item/Take Properties dialog stays open while you work elsewhere, follows changes in selected items
Pitch adjust and playrate fields accept values (such as "1.004") or simple operations (such as "x2")
+ MIDI editing
Set user-definable scales and chords in the MIDI editor for drawing and editing notes
Using mouse modifiers, copy/duplicate/paste actions can create pooled (ghosted) in-project MIDI source data
Editing any pooled MIDI media item affects all media items that share the same pooled data
Un-pool shared MIDI by gluing the media item or via MIDI source properties dialog
New MIDI Contents menu for switching MIDI editor between different MIDI media items in the project
MIDI filter improvements when displaying multiple media items in the same editor
Many new mouse modifier behaviors to paint notes and chords, edit arpeggios, etc
+ Mouse modifier customization
Customize mouse behavior when using keyboard modifiers in 40 different contexts
In many contexts, mouse click and mouse drag can be customized separately
Assign different behaviors to the mouse when over the top or bottom half of a media item
Assign any action (including custom actions) to mouse click or double-click in most contexts
Existing/legacy mouse preferences are preserved, but user changes to mousemap settings will override
Actions to reassign default mouse action for any context
Lots of customizable choices of behavior, for example:
Move/copy just the selected area of media items, or all selected media items
Edit edges/fades for all selected items, or just those whose edges line up
Adjust media item volume or pitch
Move envelope points or MIDI notes/CC just horizontally or vertically
Assign marquee selection to left-click
Assign hand-drag-scroll to right-click
Many other customizable behaviors (50 behaviors just for media items)
+ Multichannel track monitoring/input recording/routing
Allow choosing greater than 2 channels of input (inputs must be sequential, though)
Multichannel track meters
Freely route any number of track channels to other tracks, hardware outputs
+ Pitch shift envelopes
Each take gets its own pitch shift envelope, including customized range and snap settings
+ Project Bay
Manage, preview, search, replace project source media, media items, and FX
Manage media item groups and take comps for the project
Save/load project bay contents to create working sets of source media/FX for different purposes
Store sets of edited media items (including fades, stretch, pitch shift, etc) to use in any project
Media and FX+preset combinations can be stored, inserted, and switched in the project
+ ReaSurround: multi-channel surround panner with support for any number of input channels and speakers
Freely position input sources and speakers in 3D space
Configurable per-channel diffusion (treat input source audio as a shaped area rather than a point)
Drag track IO button to ReaSurround to add new input sources
+ Render and batch-convert improvements
Support for rendering project tracks and time regions to separate folders and files
Customizable wildcards provide great flexibility in naming batches of rendered/converted files
Save render presets for workflow efficiency
+ Take lanes and comping
Take lanes remain aligned by recording pass, creating empty lanes as needed (optional)
Each recording pass gets its own take lane, even when recording overlaps existing items
Recording no longer splits existing media items into different numbers of take lanes
Save/load named comps (sets of takes from multiple media items)
A/B or cycle through saved comps to audition/compare
+ Theme layout support (WALTER)
Per-track TCP/MCP layout support
Screensets support saving/restoring layouts
Old themes use default layouts available in Plugins/default_layouts.txt
New themes can define their own layouts
Layouts can be switched via menu, screensets/layouts dialog, or customizable actions
See: http://www-dev.reaper.fm/sdk/w(...)r.php
+ Time selection
Default copy/cut/glue actions respect time selection if there is one (including leading/trailing space)
Using mouse modifiers, copy/move behaviors can respect time selection if there is one
Editing behavior can be customized separately for media items, envelope points, MIDI editing
+ Track input FX chain support
FX in the input FX chain only run when record armed, and only affect the signal coming in
Input MIDI or audio, and set recording to be MIDI or audio independent of the input format
+ Track pan improvements
Track stereo width controls and envelopes
Configurable track pan modes: balance, stereo pan (L/R + width), dual pan, and classic (3.x) balance
+ Transient detection and Dynamic Split improvements
Separate threshold and sensitivity settings, and other options
+ Video: many performance improvements, support for sequencing still images
+ Volume faders: new default hardware-emulation fader taper

4.0 sub-headline changes:

+ Always-on-top (pin) button for most windows, including FX windows
+ Automute safety feature is a global setting (rather than per-project), enabled by default
+ Crossfades: separate default settings for crossfade shapes, crossfade-on-split length
+ DDP export support (thanks to Sergej Marsnjak)
+ Envelopes: configurable transition time for automatically created edge points
Allows adjusting the ramp time when editing envelope segments
+ FX: combined REAPER presets and VST patches/AU presets in a single dropdown
+ FX: user can save a preset as default, to be automatically set when inserting the FX
+ FX browser: option to display/change default preset without opening the FX
+ FX sidechains are draggable
Drag track IO button to a plugin window to add destination track channels 3+4 and create a send
+ Installer (Windows): added "portable install" checkbox and more command line options
"Portable install" will install REAPER with no icons, registry keys, or uninstaller
User preferences and settings for portable installs are kept separate
+ Live FX multiprocessing now works more effectively when tracks are in folders
+ Media item fade drawing improvements, options to prevent editing fade-in/fade-out when the item is small
+ Media item selection sets can be named/saved/loaded using the screensets dialog
+ MIDI input/output: support for up to 62/64 separate input and output devices
+ Multichannel item improvements: allow choosing any mono/stereo pair from multichannel items
+ ReaVerb: huge realtime performance improvements
+ Region Manager: basic report-style dialog to manage time regions, naming, colors, and render behavior
+ Sample rate conversion: improved sub-sample accuracy when used with project sample rate snap
+ Sample rate snap (enable in the snap settings dialog), improved sample-level display
+ Scale finder dialog: identify scales and chords based on input notes
+ Splash screen: displays when unloading projects (useful for status), other improvements
+ Time selection is editable in MIDI editor
+ Track Manager: basic report-style dialog to manage track visibility and selection
+ Track and send faders can be linked to MIDI volume/pan
+ Unlooped media item editing: dragging either edge of an item pads with silence
+ Video playback CPU/RAM/performance improvements and fixes
+ VoiceOver improvements for OSX (improves accessibility for visually impaired users)
+ WASAPI audio support (Windows), improvements to WDM/MME/DirectSound output modes

For full log see: http://www.reaper.fm/whatsnew.txt

v3.0-v3.7x - May 2009 - August 2011
v2.0-v2.5x - October 2007 - October 2008
v1.0-v1.888 - August 2006 - August 2007
v0.2-v0.999 - December 2005 - July 2006