REAPER is a powerful but sensible Windows application that lets you record, arrange, edit, and render multi-track waveform audio. It provides an extensive set of features, but is a very small and lightweight application (the installer is less than 1 megabyte, and includes many effects and a sample project).
REAPER supports ASIO, Kernel Streaming, WaveOut, and DirectSound for playback and recording. It reads WAV, OGG, and MP3 files, and records WAV files. You can arrange any number of items in any number of tracks and use audio processing plug-ins (DirectX and Jesusonic). REAPER also supports volume, pan controls and envelopes per track, multi-layer undo/redo, and user creatable color themes.

Basic features:
- Portable - supports running from USB keys or other removable media
- 64 bit audio engine
- Excellent low-latency performance
- Multiprocessor capable
- Direct multi-track recording to many formats including WAV/BWF/W64, AIFF, WavPack, FLAC, OGG, and MIDI.
- Extremely flexible routing
- Fast, tool-less editing
- Supports a wide range of hardware (nearly any audio interface, outboard hardware, many control surfaces)
- Support for VST, VSTi, DX, DXi effects
- ReaPlugs: high quality 64 bit effect suite
- Tightly coded - installer is just over 2MB

Editing features:
- Tool-less mouse interface -- spend less time clicking
- Drag and drop files to instantly import them into a project
- Support for mixing any combination of file type/samplerate/bit depth on each track
- Easily split, move, and resize items
- Each item has easily manipulated fades and volume
- Tab to transient support
- Configurable and editable automatic crossfading of overlapping items
- Per-item pitch shift and time stretch
- Arbitrary item grouping
- Markers and envelopes can be moved in logical sync with editing operations
- Ripple editing - moving/deletion of items can optionally affect later items
- Multiple tempos and time signatures per project
- Ability to define and edit project via regions
- Automation envelopes

Changes in REAPER v2.205 - May 6, 2008:
* Synchronous FX multiprocessing mode (even more) improvements/optimizations
* FX add window has options for autoclearing search field
* ReaMote: autosearch now updates open FX windows if slaves added
* internal scrolling optimizations (T,MP!)
* Navigator: fixed GDI release bug (T,MP!)
* updating track names now updates any open FX windows
* New optional automatic thread behavior mode in prefs/buffering, (less CPU and decent low latency perf)
* Improved worker thread behavior for tracks that have no items/output/etc
* Improved onscreen positioning of windows (T,MP!)
* screensets can now remember focus of main edit window, track control panels
* Big internal mac updates (may affect windows version, needs testing!)
* Option to use alternate keyboard bindings when recording
* optimized some excess refreshes when scrolling in certain instances (T,MP!)