Fast, Powerful Editing:
Drag and drop to import, arrange, and render
Freely mix audio, MIDI, video, still image media on any track
Easily move, split, glue, resize, trim, loop, time stretch, pitch shift, fade, crossfade, slip, snap to grid, without switching tools
Intuitive zoom, scroll, scrub, jog, tab to audio transient, MIDI navigation
Simple and powerful nested folder system allows group editing, routing, bussing, all in one step
Full automation recording, playback, and editing support for track controls and plug-ins
Easily manage tempo, time signature, and varispeed changes
Separate audio or MIDI into freely arrangeable takes and lanes for easy comping
Easily copy or move regions, to quickly try out alternate arrangements

Plug-in Support:
Insert almost any third-party audio or MIDI plug-in: VST, VSTi, DX, DXi, AU (OSX only), JS
ReWire (audio and MIDI) any capable application for even more flexibility
Fully automatic plug-in delay compensation (PDC)
Sidechain any plug-in, even if the plug-in does not natively support sidechaining
Apply FX in real time, or non-destructively render FX output
Real-time network FX processing: use other local machines as an FX farm

64-bit ReaPlugs Suite:
Unlimited multiband EQ with draggable nodes
Graphical FFT EQ/dynamics processing
Technical and multiband compression
Flexible, open-format convolution reverb
Real-time pitch correction, with Elastique 2 Pro built in
Multitap delay, basic synthesizer, sample player, vocoder, algorithmic reverb, and more
Special-use plug-ins to virtualize outboard hardware, stream audio, connect to NINJAM servers, and more
Includes the JS audio and midi plug-in scripting engine, and hundreds of user-programmable effects

Intangibles:
REAPER starts and loads fast - be ready to record in just a few seconds
Portable - put REAPER in your pocket and run it from a USB key or other removable media
Tightly coded - installer is only a few MB, updates can be installed in less than a minute
Rapid, efficient development - new features and optimizations are added quickly and often
Very active, enthusiastic, and helpful user forum, get help quickly
Fantastic and readable user-created manual
An honest business model that aims to provide the best possible user experience

Video:added preliminary VLC support for video playback (install latest VLC for improved video decoding)
added YV12 colorspace support for OSX, Quicktime decoding
improved bridged-quicktime behavior with mp3 audio (ignores audio rather than crashing)
OSX:
fixed play cursor artifacts with retina displays
new faster CoreText rendering used on 10.5+, more consistent text
now linked against 10.5 SDK, but with 10.4 compatibility
option to ignore CoreAudio reset messages (can enable for certain devices, emulates 4.22 behavior)
Routing matrix:
mouseover highlight of current position
improved functionality with click/drag to change multiple tracks
show MIDI inputs and outputs
improved display of MIDI-only sends
Automute:
option (default) to clear automutes on playback start
improved updating of arrange when automuting
Media items:
improved new 4.30 fade shape behavior with fully overlapping items
avoid creating tiny media items when pencil-drawing with snap enabled
MIDI:
improved linear painting in drum modes .
fixed overdub+autopunch+preroll bug
[issueid=4046]allow pasting of MIDI events directly in arrange view (adds item, or pastes in existing item)
ReaVerb:
fixed incorrect transition from mono to stereo signals with stereo impulses
corrected latency immediately after samplerate change
Track routing dialog:
improved layout when using large fonts on Windows
fixed parent channel not repopulating after adding sends
FX browser: optional alternate tree/list layout (doubleclick divider to change)

ReaStream: added localhost support for win32, improved broadcast support on OSX, improved recent host history

Time signatures: fixed adjusting media items when changing time signature numerator.