In the context of #FOSS, #opensource software, I see often the word "alternative".
This word gives me a feeling of a second choice after the "real" thing.
For example: "Zammand is the open-source alternative for help desks".
Maybe it would be better to say something like: "Zammand is the open-source solution for help desks".
Or "solution", or "application".
What do you think?
Do you have other suggestions?