I put this in Tamagotchi Cousins because it's not an official BanDai app and has no Tamagotchi characters, but it's "inspired" by Tamagotchi.
Anyway, this is my review on the app Hatchi - Free version. The paid version costs less than $1 and has a few more features than the free one, but I don't have the paid one so I can't review that.
I've only actually had the app for about 2 days so I can't say anything about evolution speed and stuff like that. I might edit the review once my Hatchi has grown up.
I think the app is available on iOS as well as Android, but I have an Android phone so not everything in this review will apply to the iOS version (whether it glitches or not and stuff like that). Anyway, here's the review:
INTRODUCTION: Hatchi is an app a lot like Tamagotchi, where you can raise a black-and-white pixel character. However, it is not quite as needy and is easily manageable if you go to school. You can choose whether you want it to display notifications or not. Hatchi has a lot more features than a basic Tamagotchi, it's an app, the evolution speed is different and it has different characters and icons. Those are the only real differences to a Tama.
HOW WELL IT WORKS: On my phone (an HTC Desire C) Hatchi Free works perfectly, except that sometimes when I quit the app it pauses. The trick to stop it pausing seems to be to go to the main screen of the game and exit it before turning your phone off. Also, sometimes it does not send notifications when it should. It doesn't appear to slow down my phone or take up a lot of battery power either. Hatchi Free does have ads, but they don't pop up often and when they do, they don't get in the way.
WHAT FEATURES IT HAS: Hatchi has some features Tamagotchi doesn't have. It has about 5-9 games (I haven't counted), although some can only be played on the paid version. Your character is either a boy or a girl, you can name it, its blood type is specified and it has a set trait (mine is "Heroic" for example). There are various stats you have to increase - Hunger, Hygiene, Active, Smart, Happy and Energy. Hunger is filled by feeding it; Hygiene by cleaning it the same way as you do to a Tama; Active by playing games; Smart by giving it a book to read; Happy by doing anything with it; Energy by letting it sleep. There is a shop where you can buy backgrounds for the Hatchi's screen, re-colour and personalise your Hatchi and buy food for it (although free food is always available). Also, you can abandon a Hatchi, which is basically the same as resetting except you don't lose money.
That's just a basic review of the app, if you want more detail on it you can PM me and I'll send you a more detailed review. Overall, I recommend this app, but I don't know if the paid version is worth it.