Can I count my contribution to the open source as a dharma? It is mean, that if I am professional developer and I can help other people for free, can I think, that software development, that is my hobby and profession, in the same time is my Dharma?
Open source is awesome philosophically speaking, and that's really what counts in the dharma, not the actual benefit that accrues to others. A core tenet of Buddhism is to not cling:

&quot;And he clings to nothing in the world.&quot;
-- The Buddha (MN 10)

So, regardless of the nature of your work, the fact that you are able to give up your attachment to its ownership is positive. If, for example, you produce pornography or a drink-mixing app, well, that's bad. If you make it open source, that is good, since the alternative is to cling to it.
Some years ago, a Buddhist monk threatened me with legal action over a text translated from the Pali 60 years ago that his organization owned the copyright to and which I had posted on our website in HTML format. It was remarkable to note at the time that people in the FOSS (Free and Open Source Software) community sounded more Buddhist than the Buddhists. Mark Shuttleworth, for example:

That’s the magical thing about creation and ownership. It creates the possibility for generosity. You can’t really give something you don’t own, but if you do, you’ve made a genuine contribution. A gift is different from a loan. It imposes no strings, it empowers the recipient and it frees the giver of the responsibilities of ownership. We tend to think that solving our own problems to produce a patch which is interesting to us and useful for us is the generosity. It isn’t. The opportunity for generosity comes thereafter. And in our ecosystem, generosity is important. It’s at the heart of the Ubuntu ethic, and it’s important even between competitors, because the competitors outside our ecosystem are impossible to beat if we are not supportive of one another.
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Or Richard Stallman (admittedly, not the best Buddhist role model):

I'm often asked to describe the “advantages” of free software. But the word “advantages” is too weak when it comes to freedom. Life without freedom is oppression, and that applies to computing as well as every other activity in our lives. We must refuse to give the developers of the programs or computing services control over the computing we do. This is the right thing to do, for selfish reasons; but not solely for selfish reasons.
Freedom includes the freedom to cooperate with others. Denying people that freedom means keeping them divided, which is the start of a scheme to oppress them. In the free software community, we are very much aware of the importance of the freedom to cooperate because our work consists of organized cooperation. If your friend comes to visit and sees you use a program, she might ask for a copy. A program which stops you from redistributing it, or says you're “not supposed to”, is antisocial.
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So yeah, the FOSS movement is awesome; a lot of open source advocates are Buddhist, or at least Buddhaphiles. There's even a Bodhi Linux, for example. It runs on the Enlightenment desktop. Actually, I'm not sure if that's dharmic or just crass...
I think you have one too many commas in your question, but if you are asking whether software development is dhamma practice, then I guess the answer is that the part of it that is you letting go of your attachment to stuff is dharmic. Coding software itself is not the same as developing your mind towards enlightenment, though...