A few days ago a one of my friend asked me to recommend some online diagramming tools if I know. But only tool I new about is the diagramming options available on Microsoft Office. But it has limited features and can access by only one person to my knowledge. Based on my research I found diagram drawing tools that are collaborative and access from any where.
Though these tools you can draw, edit, save and share your diagrams like flowchart, network diagram, wireframe, Organizational charts etc. Most of them have free basic option or free trail that you could use and experience these tools.