I just wondering, whether anyone agree if I say that software (beta/prototype version) download number as an achievement for a software product, especially in startup stage.
I know it is not a real sale, but at least some people are willing to try the software, this also means there is "real" market for the product.
Another question: Can I use this beta download statistic in business proposal to get funding?
To a point, yes. The number of downloads is a statistic alright! But ask yourself if this is "Viable". It won't be as accurate as number of sales because anyone can download the product with no intent of purchasing it. You probably have competitors and they might have a premium product and you haev a freemium product. People who do not want to pay for the same thing might come to you and download the product. If you start charging as well, then there is no guarantee that they will buy your product or move on to a new competitor who is giving a freemium.
You need something more solid, it might be a good achievement but it wont seduce your investors.
You can certainly use such a number in a business plan/proposal when you're looking for investors, but you shouldn't use it all by itself. The real question is what percentage of beta users are willing to upgrade to a paid version after testing the software, especially if you're going after the freemium or trial marketing model.
You could find out how many users are willing to upgrade after trying out by sending your current beta users a no-commitment inquiry/survey. Ask them to provide feedback about the product with a few short questions; among those, one yes-or-no question about whether they would be willing to pay a certain fee to continue to use it. If the results are good, you can use that percentage in your argumentation with potential investors, and you could even factor that into your financial projections ("x% of all trial downloads will likely convert into paying users").
Just my 2c, hope it helps.