Mac MKV Player Freeware (1) - VLC
Using VideoLAN VLC Media Player - VLC player supports all the video and audio streams you will find in an MKV file. You need not to install any codecs or filters to play .mkv files.

About VLC Media Player
VLC media player is a highly portable multimedia player for various audio and video formats (MPEG-1, MPEG-2, MPEG-4, DivX, MKV, MP3, OGG, ...) as well as DVDs, VCDs, and various streaming protocols. It can also be used as a server to stream in unicast or multicast in IPv4 or IPv6 on a high-bandwidth network. It doesn’t need any external codec or program to work.

Free Download VLC Media Player

Free MKV Player for Mac (2) - MPlayer OS X

Media Player Classic has a built in DVD player with real-time zoom, support for AVI subtitles, QuickTime and RealVideo support (requires QuickTime and/or Real Player); built-in MPEG2/SVCD/DVD codec. To play mkv file you need to install updated Matroska Pack. To do so follow simple steps below:

Open Media Player Classic and navigate to View –> Options then Select Internal Filters situated on the left and then uncheck to disable Matroska. Now Install the Matroska Pack. You should now be able to play the mkv files.

Free Download MPlayer OS X

What’s MKV format

MKV is a container format developed by Matroska. It can hold different types of video and audio. For example, there might be an .avi file contained within the .mkv file.

The Matroska Multimedia Container is an open standard free Container format, a file format that can hold an unlimited number of video, audio, picture or subtitle tracks inside a single file. It is intended to serve as a universal format for storing common multimedia content, like movies or TV shows. Matroska is similar in conception to other containers like AVI, MP4 or ASF, but is entirely open in specification, with implementations consisting mostly of open source software. Matroska file types are .MKV for video (with subtitles and audio), .MKA for audio-only files and .MKS for subtitles only. High Definition movies in 720 or 1080 pixel width format are often encoded and packaged as a Matroska format video with a .mkv file extension.

Matroska file types
.mkv : Generally video files, as well those containing audio ( movies ) or video only.
.mka : audio only files, can contain any supported audio compression format, such as MP2, MP3, Vorbis, AAC, AC3, DTS, PCM and soon MPC ( musepack ).
.mks : a so called ‘elementary’ matroska stream containing any subtitles stream.

Resource: http://aimersoft-mac.com/articles/free-play-mkv-on-mac.html

Step1. Install Total Media Converter for Mac
Download and install Aimersoft Total Media Converter for Mac
click the "Add video” button to import your WMV video, this Total Media Converter for Mac support batch conversion, so you can import multiple files at a time

Step2. Convert WMV to MP4, WMV to MOV, WMV to AVI/MPEG/MP3/AAC/etc

Check the files you want to convert, and then click the “Settings” button to select output formats. There are some categories such as common video, common audio, iPod, iPhone, PSP, or you can customize the formats according to your need.

After the above steps, you can click the “Start” button to finish the conversion.

Tips:
1. Open the “Edit” section to edit your WMV file, you can trim a part of WMV file, or cut off the black edges of your video, or add watermark to your video for sharing.
2. If you want to join some WMV files to one file for playback on your iPod, iPhone, PSP, or other portable devices, you can check “Merge into one file” on the main interface of this software.

3. You can use Total Media Converter for Mac to convert DVD and video files, and output them to ome file.

4. If you have other video formats, such as MKV, TS,TP, MTS, M2TS, TRP, FLV, MP4, MOV, AVI, Mod, ASF, etc,  Total Media Converter also can help you convert them to your need formats.

Resource: http://www.aimersoft-mac.com/articles/convert-wmv-mp4-mov.html