If you are looking for an alternative to microsoft visio take a look at draw io
Its web based, free and very much straight forward tool – no registration or login needed, which is nice.
Well its not as powerfull with all the shapes microsoft visio has, but you can do a lot. Flowcharts, Diagramms and so on. Its definitely a glimps worth.
I have just created a network schema which i will show you in the next post.