Following are some very useful websites.
Chrome Extenstion – Vysor
desmos.com – For Maths, Graph, Art, Analytic
placeholdit.co – for setting place holders for images.
scribbless.com – for managing lists online
gtmetrix.com – To optimize website, first have review of site performance at
pixlr.com – online image editors
PDF info changer – edits pdf metadata, free utility