ManualsLib - Just enter the keywords in the search field and find what you are looking for!
ManualAgent - Manuals and guides
Manuzoid - Repository that includes user manuals for various products
Internet Archive Manual Library - Internet Archive Manual Library is your go-to source for viewing the big collection of datasheets, instructions, and guides written for a wide range of products.
Manula - Manula is an online software for creating user manuals.
Stonly - Create interactive step-by-step guides