Share Keyboard/Mouse between PC (windows?) and Android

I searched for ages for this very same thing. I found the Share Keyboard & Mouse app (by SmartUX) on the Google play store which should do what you want. You can find the PC client on their web page.

I was looking for the same thing, after a long search I found a little known piece of software that does the work nicely over Bluetooth for android/windows/Mac. The android client is even updated this year.

Acrosscenter

I have it working with a Samsung Galaxy Tab 2 10.1 (rooted with CM12) and windows 7.

I was also looking for such a solution that would allow me to share my computer's Mouse and Keyboard with my Android devices. I was using ShareKM until it was abandoned and no longer worked on recent Android versions.

Eventually, I developed my own solution, DeskDock, that works on all major Desktop OSs (Windows, Mac, Linux) and with all recent Android versions (starting from 4.1). It does not require root access and provides advanced functions such as drag and drop.

I just released it a few days ago to Google Play.

I realize the question was about a software solution but I just came across this Matias keyboard the other day. That looks like would work for this question.

They market it for iPhones but it looks like it will work with Android devices as well:

Also connects to other devices.
We designed the keyboard to connect wirelessly to your iPhone, but it's actually a standard Bluetooth connection, so it'll work with any device that supports Bluetooth keyboards.

That includes... the iPod touch, iPad, Macs and PCs, Android 3.0+ smartphones and tablets, Samsung Galaxy Tab, BlackBerry PlayBook, and many more.