[Google Chromecast] Asphyx:
The other options out there (BubbleUPnP and PlayOn being the closest to mirroring what Plex does) do not have all the features Plex does.

Some however have features that Plex does NOT have such as playing content stored on your Mobile device locally. Plex removes the need to ever store content on your mobile device since it works as a Home Cloud for Media available anywhere you have access to the Net.

And while Bubble and others may be able to send ON UNIT content to the CCast it won't do it unless the Source is CCast compatible.

Bubble does have the ability to transcode if the content is coming from the Bubble Server (on the Desktop) but I'm not sure it will transcode ON UNIT LOCAL files when sending to CCast. Perhaps it does but it would require sending the file from your phone to your desktop then sending it to CCast. You should ask the Dev for Bubble to clarify this they post here regularly and are very responsive to their Users. (I have Bubble running myself on the same server as my Plex. and It's a very good alternative for Plex.)

Apps like aVia and Real Player are all very limited to playing content either on a cloud or locally on the the device.

Great if you have everything you want to view locally or synced to the cloud but hardly gives you the TBs of data that my Plex makes available to me.

Plex is perhaps a bit pricey right now since CCast support requires PlexPass but there is a way around that using Bubble UPnP until such time as CCast support no longer requires PlexPass.

Set up the Plex Server and also set up BubbleUPnP and let it aggregate the Plex Media Server library.

Then use the BubbleUPnP on your mobile device to send to CCast.

Bubble Server will transcode for you and you can still use the Plex for Android App (Paid app like aVia) for viewing on your mobile device if you like.

Once the CCast options go public you can decide which interface you like better.

Right now I have PlayOn, BubbleUPnP and Plex server all running on the same machine.

I rarely use anything aside from Plex since I have Plex Pass.

[EDIT/UPDATE]

Ok just went to Plex and found out that Direct Play is NOT currently supported the direct play entry was left in the profile by mistake.

It will however stream and has added a new streaming protocol that allows MKV to play without a heavy transcoding thread being needed for sources that are codec compatible (H.264/AAC)

The Player must support the DirectPlay (which may happen in future) and if it can't it will kick it back to the transcoder for streaming.

All direct Play is determined by the Player not the server so if it tries to direct play and fails it fallsback to the transcoder.

Bottom Line though is that Matroska is now supported in profile and will stream much better provided the codecs do not need changing.

And as with any container, Multiple Audio Tracks will always require transcoding to select which Audio track to play. So unless you want the first Audio Track you will probably still be using the full on Transcode.

All of this can change in the future if and when they update the CCast Player App to support more containers via Direct Play and Track Selection on the Client side.

But they are not there yet.