This is the Wi-Fi / Wi-Fi Direct based peer to peer communication framework for Android. It stands for "Croconaut Public Transport", Croconaut was a "startup" from the times when we thought we can finish the product in three months. :)

Checkout the wiki for detailed description and information or follow the quick step-by-step guide and surely take a look at WiFON mini with a small demonstration how to put all together:

Gradle

repositories {
    maven {
        url "https://mymavenrepo.com/repo/fsD4SRhSQewcguNLyevk"
    }
    maven {
        url "https://s3.amazonaws.com/repo.commonsware.com"
    }
}

dependencies {
    compile 'com.croconaut:cpt:1.0.16'
}

Add the broadcast receiver

AndroidManifest.xml:

<receiver android:name=".MyBroadcastReceiver" />

MyBroadcastReceiver.java:

import com.croconaut.cpt.ui.CptReceiver;

public class MyBroadcastReceiver extends CptReceiver {
    // implement the interface, most important functions are:
    @Override
    protected void onNearbyPeers(Context context, ArrayList<NearbyUser> nearbyUsers) {
        // NearbyUser.crocoId shall be used as the recipient's ID
    }
    @Override
    protected void onNewMessage(Context context, long messageId, Date receivedTime, IncomingMessage incomingMessage) {
        // read / request attachments and get your app data (like a text message)
    }
}

Register the broadcast receiver and username

Communication.register(this, "Miro Kropacek", MyBroadcastReceiver.class);

Enable CPT

Technically speaking, you don't have to enable CPT if you don't want to transmit it immediately, the message will be stored anyway.

CptController cptController = new CptController(this);
cptController.setMode(LinkLayerMode.FOREGROUND);

Send a message

OutgoingPayload outgoingPayload = new OutgoingPayload("Hi there from the other device");    // can be anything Serializable, not only a string
OutgoingMessage outgoingMessage = new OutgoingMessage(targetCrocoId);
outgoingMessage.setPayload(outgoingPayload);
Communication.newMessage(getContext(), outgoingMessage);

Source code release

Please note that you need to supply your own google-services.json file and possibly myMavenRepoWriteUrl if you want to deploy the archive.

Also, the library isn't 100% ready for targetting API > 22 because it still relies on the static permission model (among other things, there seem to be some issues with notifications, too). So if you plan to release your app on the Play Store, you need to change CPT internals in a way that you can use the dynamic model. Pull requests welcome. :)