I feel overwhelmed for the acceptance rate of some conferences
I know the feeling. I have just a few days ago received a reject (with mostly positive comments) from a conference with an acceptance rate of less than 14%. Happens to the best of us. (or more accurately, it mathematically has to happen to most people most of the time, otherwise you can't end up with such low acceptance rates)
If I submit a "short paper" rather than a regular one, Will that make easier to get accepted?
Generally yes, but the "short paper" tracks at some conferences have in the mean time become viciously competitive as well. In one major conference in my field, the acceptance rate for work-in-progress papers is nowadays below 20% as well.
By and large, whether you should submit a short paper or a full paper (potentially at a weaker conference) depends on how mature your work is. A short paper at a strong conference has good chances if it is ongoing work with very high potential; mediocre finished work is likely to be rejected as a full or short paper at such venues. You have better chances if you submit a full paper to a weaker conference in this case.
My research is a software artifact that has been tested (not only unit-tested, but integrated in a bigger architecture and proved to be compatible with external applications) but not evaluated by a broad audience of users.
In most fields, whether your component is "compatible with external applications" or whether it has been "evaluated by a broad audience of users" are not the core questions for scientific merit. There are almost infinite "software systems" out there for which both of these properties are true, and which are scientifically still entirely irrelevant (pretty much all standard software, for instance). More relevant is whether the research question underlying your work is interesting, and whether your work in its current stage is able to sufficiently and convincingly answer this research question.