Logic Pro X is a DAW/MIDI sequencer for Mac OS. It has been in the works for a very long time, and is known for being highly refined and pretty easy to pick up for beginners.
SpecsUpdate
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Pros

Pro High quality instruments and effects
Good range of high quality synths: analog, FM, wavetable, string modulation, sampler, organ, clarinet, epiano.
Pro Cheaper than similar programs
This program costs US$200 and must be bought from the app store.
Pro Comes with 57gb content
The initial download of Logic Pro X gives users 2gb of samples, but the DAW automatically downloads 57gb of samples once the Logic Pro X DAW is installed.
Pro Free corresponding iPad app
In order to allow more control, the Logic Pro X DAW has added a free iPad app called Logic Remote.
Logic Remote is available in several different views, and is capable of MIDI input and parameter adjustment. It comes with a full library and browser. Navigation is easy as well via the navigation bar along the top of the screen.
Many interesting views are available, such as chord strips. This view allows users to play a series of preset chords that are already in the right key. Gestures are supported with this app, so loop speed and other properties can quickly be adjusted.
This app connects to Logic through WiFi, so the app and program should be running on the same network.
Pro UI designed for ease of use
The Logic Pro X DAW has made an effort to keep clutter out of the equation so producers can focus on the music.
Pro Studio standard
If you take music production seriously then one day maybe you'll enter professional studio, where you will most likely find the Logic DAW along with Pro Tools.
Pro Uses minimum amount of CPU
The Logic Pro X DAW is optimized for CPU usage, which makes the DAW more stable.
Pro Free update from Logic
As of 1/21/2015, Apple has released an update that allows users to upgrade from Logic to Logic Pro X.
Pro Allows users to program their own tools
The Logic Pro X DAW lets users make their own effects using with javascript leveraging its Scripter API.
Pro Easy to learn, makes writing easy, and keeps technical in the background
It is easy, intuitive, and easy-to-implement.
Pro Supports expressive MIDI - MPE
Works with new controllers like Seaboard Rise, Linnstrument, Continuum Board, etc.
Pro Full external MIDI support
Poly aftertouch, sysex and two modes of controlling external midi instruments.
Pro Does a lot of work for you
Switch in to Alchemy on the synth and you get an intuitive template to adjust wavetables and eq visually, plus various modes and styles. Handy tool.
Pro Many instruments
Different kinds of instruments all around.
Pro Many plug-ins
Pro Incorporating iOS devices, accessing Apps/Synths/Effects
A totally overlooked feature....
The Setup is as Easy as Pie.
Create an aggregate audio setup and midi device incorporating your iOS devices and wham bam....Instruments / Audio / FX all accessible within logic.,
An AU... An Audio I/O.. Brilliant.
Pro Virtual Drummer
Allows to create high quality drum tracks even if you are not a drummer.
Pro Used by celebrities
This includes: Prodigy - Invaders Must Die (everything except guitars), John Powell - How to train your dragon, other works, and Tycho (until 2011 when he switched to Reaper to finish his album). Though , Still to this day uses Logic for composing.
Lets also not forget Boris Blank that in essence is Yello, and One of the pioneers of electronic based music.
Pro With Pro Tools it's the DAW mainly used in professional studios
Cons
Con Only compatible with Mac
No Windows or Linux versions are available.
Con No support for 32-bit plugins without 3rd Party Plugin 32 Lives
Con Unusable with lots of plugins: stutters and clicks
Con Poor audio editor
Audio editor is a lot less intuitive and accessible than other DAWs.
Con Rarely updated
Since Apple purchased this software, the updates are rare and none. The latest update was less than great and has forced users to look elsewhere, especially the Pro community.
Con Not open source
Con Lags or crashes often
This happens usually when there is a lot going on in the track.
Con It is next to impossible to organize your mixer channels
There are lots of work arounds, but a straight rearrange the mixing channel would be appreciated.
Con Too big
The app is too big!
Con Very buggy
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