Visio is a great tool for creating diagrams, flowcharts, prototyping, etc. But it is Windows-only and is not free. Are there any graphical tools for Linux that can do many of these same tasks well?
There's Dia.. Not nearly as many features as Visio, but does diagrams: http://live.gnome.org/Dia
How about Pencil?
Note: KOffice, as well as some of its applications were recently renamed. KOffice is now called Calligra Suite and Kivio is called Calligra Flow. However, there has not yet been a release since the rename.
draw.io works on Linux, is free and supports either local saving, or you can save Google Drive, OneDrive and Dropbox.
WireframeSketcher is a cross-platform tool that can be used for prototyping.
I'd like to throw in yED which works on linux too, and has some nice features. It isn't GPL'd though,.
For UML and DB Diagrams, you could use UMLet.
You can find all the open source alternatives to visio here http://www.osalt.com/visio and any other equivalent for a commercial software
Lucidchart is an online alternative to Visio. It imports and exports Visio files and has a free option.
I found THIS link, you should find all the alternatives there. good luck!