Pedometer Pets

Pedometer Pets are not usually ones that require feeding and care, but are more or less a fun companion to have with you while you walk. Some just have goals, some let you interact with your pet, and some are full games based on the pedometer.

Digivices and Digimon Pendulums will not be counted here since they fall under the Digimon umbrella.

Yokaizer
ヨーカイザー

Select a place in Japan to start out in, and then travel the country capturing Yokai.

Encountering a Yokai will prompt a small battle to begin to determine if you are successful or not (it's a 50/50 shot).

This is a very fun little pedometer. A bit loud, but can be silenced, and it won't skip the Yokai encounter without your input.

Comes in multiple colors, but the shape is always the same.

Instructions

Denpa Yokaizer
電波ヨーカイザー

Appears to be related to the previous Yokaizer, but newer. The interface and programming are different, and the Denpa uses an accelerometer instead of a pendulum to count steps.
Unfortunately the accelerometers in most of these seem to no longer function properly, meaning I have no information on how it works (nor can I find anything about it).
Until I can find a way to replace this, I'm stuck without any gameplay information.

Pokemon Pikachu
Pocket Pikachu

The Pokemon Pikachu is very well documented and a very well known pedometer pet. Walk to earn Watts to gift to Pikachu in order to get it to like you! Different animations will play depending on how many Watts you have given your Pikachu, and he will leave after you've hit 1 million steps.

Instructions via Serebii

Pokemon Pikachu 2
Pocket Pikachu Color

Very similar to the original, except in color and with a new (non-slots) mini game.
In addition, you can give/receive Watts from another Pokemon Pikachu 2 as well as sending Watts to a copy of Pokemon Gold or Silver using the IR Port on the Game Boy Color.

In addition, this version has 6 different shell colors!

Instructions via Serebii

Arukundesu
あるくんです

A very in-depth pedometer based on the Dungeon Quest series where you take your slime around dungeons in order to change into different slimes! There are three different versions, 1998, 1999, and 2011, but they all work very similarly.

The dungeons are very involved and there's a lot to do in this pet!

Instructions

Pooh Walker

A super cute little pedometer that lets you pick between English, Japanese, and Chinese for your menu.
You put in information and set a steps per day goal.

Teku Teku Angel
てくてくエンジェル

As you walk, your little buddy can evolve into different forms!