"We usually make flowchart using some wordprocessor or DTP software or something like Visio. These are quite awkward to use..."

There's the understatement of the year!!!

Trying to do flowcharts in a wordprocessor is total madness!!!
Vector-based DTP is a bit better, but fails at the concept of connections - which is absolutely fundamental to flowcharting! (if you move a box, you want all its connecting lines to stay connected!)
This is not a criticism of DTP - it's just not intended for this job.

"...or like Visio quite costly."

The real joy of Visio is that is does understand connections!
Sure, if all it did was flowcharts it'd be a very expensive flowcharting tool! But it does the complete gamut of engineering, software, and business diagrams - which makes the "bang-per-buck" look a lot more favourable!

The amount of time & frustration you waste trying to do flowcharts (or just about any sort of serious diagram) in MS-Word would very quickly pay for several copies of Visio!

Surely one of the distinguishing marks of a professional is that one has and is proficient in using the correct tools for the job?

Oh, did I mention that I like Visio...? ;-)