lolz, had to check if goat tracker was ported to android and found this:
Goat Tracker https://play.google.com/store/apps/details?id=com.sbumpkin.goat
Description
Goat tracker is an application to help a farmer track when a goat should come into heat based on the last heat date.
If the farmer has bred the goat then it will calculate the earliest date to draw blood to check for pregnancy.
If the goat is pregnant it will calculate the approximate due date.
This is bound to be a long rant from me. Sorry about that 
The short version:
Regarding rules/restrictions for chipmusic. I feel that is something that is constantly evolving so in the end the most important thing is that the music feels right. Keep it simple. Arpeggios are you friend
The long version:
The thing is, chipmuisc is not ONE specific sound…
When I started making chip music on the Amiga back in the day the guidelines I went by were pretty much given: .mod-fileformat and 4 channels were the general hardware and software restrictions of the time. On top of that you should try to keep the final file size south of 20kb.
The file size restriction pretty much eliminated decently sampled instruments so instead you’d draw your own little waveforms by hand since the software did not generate stuff like that for you.
The channel restriction pretty much forced you to use arpeggio-chords since each note took up one channel, and you only had four to work with.
So those were the first restrictions I worked with.
Here you have some good examples of the Amiga 4chn mod-chip sound:
Radix “Paul the penguin”: https://www.youtube.com/watch?v=CsAPmo-fkqE
4-Mat “LFF”: https://www.youtube.com/watch?v=zlUFYMRNkPw
Emax “Digital bass-line”: https://www.youtube.com/watch?v=m1-fVb9vZDE
Later I moved from Amiga to PC. To begin with I continued working with my old restrictions but after meeting a fellow PC chip composer at a demoparty I got encouraged by his multichannel .xm-tunes to evolve.
On the PC you could use up to 32 channels. And on top of that the .xm-format gave you more effect columns and volume/pan envelopes which made it easier to tweak the sounds.
The file size got a bit bigger with the additional channels but nothing crazy. I seem to recall thinking one of my tunes that ended up about 100kb was humongous
I continued working with about the same sorts of tiny hand drawn waveforms so that part of the sound was pretty much intact. I fondly remember when I used a sampled cymbal in one song and my fellow chip musicians of the time were not too keen on that addition to the sound. …so that experiment went out the window pretty fast… 
With the 4 channel restriction lifted I often used “real” chords in combination with the arpeggios. That together with enough channels to make echoes as well as phaser/flanger like detune tricks made the .xm-tunes sound more refined and bigger than the Amiga tunes.
Here are a few good examples of the PC multichannel xm-sound:
Radix “The Mission”: https://www.youtube.com/watch?v=QQxo9WG7Ktk&list=UUYZIBGsbFxj9EDsaU67oJ-g
Loonie “Contemplated”: https://www.youtube.com/watch?v=IXzAjQeLD08
Zabutom “Final Blast”: https://soundcloud.com/zabutom/final-blast
I had along brake from chip music between 2000-2010. When I finally came around and felt like doing some stuff again I took a look around to see what had happened the last decade… And things had changed a lot Softsynths, tweaked gameboys, post processing and stuff like that.
Now a days I don’t care much about file restrictions. I often use fitting samples regardless of size, but I mix and match with old style hand drawn waveforms.
Lately I have started doing some post simple processing and mixing outside the tracker to give the tunes a bit more clarity and punch. Thats something I never did back in the day but since mixing in the tracker can be cumbersome I finally ended up going the “easy route”
Since I tend to enjoy working with layers I mostly use lots of channels but now and again I want to challenge my selfe and then I go back to the 4 channel restriction.
…but the thing is… I entered a old school music comp last year and thought it would be fun to use the 4 channel less than 20kb restriction so I went for it. Managed to do a song like that and entered the comp. …and at the party I was talking to a c64 guy about my tune and me working with restrictions. He just smiled at me because on the c64 you only have 3 channels and less memory…
Sooo… Chipmusic and the chip sound is not just ONE thing. Not just one set of restrictions. Just try to keep it simple and have fun.
If you are interested here are some chiptunes I have made:
4 channels .xm: https://soundcloud.com/gusse_dsx/cracked-nostalgia
4 channels .xm: https://soundcloud.com/gusse_dsx/dandelion-shuffle
4 channels .xm: https://soundcloud.com/gusse_dsx/minor-problem
12 channels .xm: https://soundcloud.com/gusse_dsx/digital-vacation
24 channels .xm: https://soundcloud.com/gusse_dsx/legacy-system-anthem
24 channels .xm: https://soundcloud.com/gusse_dsx/intergalactikus
32 channels .xm: https://soundcloud.com/gusse_dsx/rusty-robot