Audacity is a free multi-featured multi-track sound editor and DAW for MacOS, Windows, and Linux. It can record directly or import WAV, Ogg Vorbis, MP3, AIFF, and many other formats. Features include builtin effects, VST plugin loading, fast editing, and unlimited undo.

Features:

• Record from microphone, mixers, cassettes, records, minidiscs, FM radio… Scheduled recording feature.
• Import sound files, edit them and mix with other files or new recordings. Export to several common file formats including WAV, AIFF, FLAC, MP3 (with optional LAME library), AAC (import only).
• Fast sample-level editing with Cut, Copy, Paste and Delete, and unlimited Undo/Redo. 32 bit float internal storage and high quality resampling and dithering. Smooth volume envelope.
• Many more features.

Related Hardware:
To record audio you will need an Audio Interface: See our review of USB Audio Interfaces here.
DAW Controller Roundup

Changes in v2.1.2:

• New option ‘Spectral Reassignment’. This algorithm deduces a ‘finer’ spectrogram for vocal work.
• Improvements to Pitch (EAC) – cleaner (sharper) display.
• Spectrogram Settings are now available per-track.
• Upgraded the key wxWidgets library we use from version 2.8.12 to version 3.0.2 to fix Linux related bugs

Changes in v2.1.1:

• Track seeking and scrubbing
• Quick-Play
• Improved Draw Tool and zooming of spectrogram
• Improved effects plug-in
• Various bugfixes and interface improvements

Changes in v2.1.0:

• Built-in effects were improved.
• Redesigned and improved interface
• Operating system and sound device support changes
• Various bugfixes

Changes in v2.0.6:

• Improved interface
• Improved effects
• VST effects now support standard FXP presets
• LV2 effects supported on all platforms
• Various bugfixes

Changes in v2.0.5:

• Fixed crashes when importing audio files
• Finder "Open with" now working, double-clicking or dragging files to the Audacity icon will open them.
• Faster startup and avoids crashing by delaying the loading of Audio Unit plug-ins until they are used.
• Fixed shaped dither being too loud
• Improved tracks menu and label editor.

Changes in v2.0.3:

• Uses libsoxr resampling library by default, instead of libresample, for higher quality and speed.
• Bugfix for Time Tracks and improvements
• New effects: "Studio Fade Out", "Adjustable Fade" and "Bass and Treble"

Changes in v2.0.2:

• Bugfix for Timer Record: Interlinking of the Start, End and Duration controls.
• Bugfix for Normalize crash
• Bugfix for clicks on split lines
• Improved toolbars
• Enhanced some Nyquist effects

Changes in v2.0.1:

• Audacity now has excellent compatibility with the VoiceOver screen reader.
• Selection Toolbar: a value for the previous whole second displayed if the value was close to a whole second.
• Finding zero crossings could cause the selection to expand into white space at either side of the clip.
• Clips did not drag to another track if mouse was over a selection.
• Mixer Board: Rendering four tracks resulted in a redundant Track Strip followed by a crash.
• Imports, Exports and Files
• Exporting to WAV or AIFF led to a "Libsndfile says" error or corrupted output due to order of metadata in imported files.
• BugFix for crashes importing MP3 files on PPC machines.
• Bugfix for issues where normalization could be to wrong value if applied with DC offset correction, or if applied to "read-directly" WAV and AIFF files
• Sliding Time Scale: fixed an audible discontinuity at the beginning of the processed selection; fixed a serious quality problem on Linux 64-bit.
• Bugfix to prevent zooming with mouse wheel or ball scrolling the content off-screen.
• Shortcuts can now be added in Keyboard Preferences to items in the Generate, Effect or Analyze menus, including user-added plug-ins.
• Nyquist Effect plug-ins can now be added to Chains.
• New "Paulstretch" effect for extreme slowdown without pitch change.
• New "Sample Data Export" Analyze effect for exporting a file containing amplitude values for each sample in the selection.
• New Preference (off by default) to import files On-Demand (without seek ability) when using the optional FFmpeg library.
• New Preference (off by default) to retain labels when deleting a selection that snaps to the label without extending past it.
• CleanSpeech Mode (no longer supported)
• Added Serbian (Latin and Cyrillic) translations.

Updates in v2.0:

• Replaces Audacity 1.2.6, Audacity 1.3.14 and older versions
• Many effects were enhanced
• Equalization, Noise Removal and Normalize heavily improved
• Vocal Remover now included plus GVerb on Windows and Mac
• VAMP analysis plug-ins now supported
• Improved label tracks with Sync-Lock Tracks feature in the Tracks Menu.
• New Device Toolbar to manage inputs and outputs.
• Timer Record feature.
• New Mixer Board view with per-track VU meters.
• Automatic Crash Recovery in the event of abnormal program termination.
• Fast "On-Demand" import of WAV/AIFF files if read directly from source.
• FLAC now fully supported
• Added support for optional FFmpeg library
• Multiple clips per track
• Bugfixes for playback speed, synchronization and shortcut use
• Bugfixes for file imports and exports
• Bugfixes for analysis and effects
• New interface preference to show the track name in display
• Restored use of Page Up/Down to scroll horizontally
• Longer default playback preference for effects preview

New in 1.3.14 Beta :

• Bugfix for handling corrupted project files
• Bugfix for Plot Spectrum to preserve signal level if multiple tracks were analyzed
• Bugfix for crashes when dragging tracks and resetting toolbars
• Bugfix for MP2 files import.
• Bugfix for the excessive delay that occurs when typing into labels in long projects.
• (OS X) Added support for AudioUnit MusicEffects (but no MIDI support)
• CleanSpeech Mode has been removed from Preferences but can be run or disabled in 1.3.14 by changing Preferences in a previous Audacity version
• Mix and Render now preserves clip length by not rendering white space before the start of audio, and preserves audio before time zero
• Spectrograms now allow window sizes up to 32768 and frequencies up to half the sample rate (the maximum possible)
• Normalize now preserves left-right balance in stereo tracks by default with an option to normalize stereo channels independently.

New in 1.3.12 Beta :

• VST Effects now display GUI by default
• Faster Equalization and Noise Removal; improved Truncate Silence and Click Track
• Chains applied to files now clear temporary data after processing each file
• Updated Nyquist implementation with support for SAL syntax and improved memory management
• Plot Spectrum now analyzes up to 237.8 seconds of audio, with separate windows for each project and improved display; new preferences for Spectrograms
• Contrast Analysis tool now modeless for easier use