I've looked for a feedback form that shows up in the bottom-left of the page, but all I've came across were simple feedback forms or forms that required a subscription (like $29 a month).
I've decided to do one myself, and here it is.
Place all this code anywhere between the <body> tags. Remember you still have to include the jquery library.
You can easily change the stlyle of the form, the messages that appear, time after the form shows up, etc... Just look through the source files.
I've also created the PHP that handles the feedback sending through e-mail.
Remember to replace the e-mail in the .php file with yours.
If there's anything unclear or you have any question post in the comment section below.