What is a variant offer?
Ok, I explain it to you without so much formal roll. A variant offer (or alternative, which is the same) is basically when a company, instead of limiting itself to what the government asks in a public tender, says: "Hey, and if we do it otherwise, that the same is better or cheaper?" It is not that they send a separate proposal, but, together with the main offer, they put this kind of “plan B” that has to meet, yes or yes, with the minimum requirements of the contest.
The grace of all this is that companies can show off: they propose new ideas, more cool solutions, or different technologies that had probably not even occurred to those who wrote the specifications. That, in the end, helps the process to be less boring and more competitive, and sometimes the administration ends up caught something better than I expected.
Of course, eye: they don't always let you present these variants. It depends on what the sheet puts. There are competitions where, they give you free way, and others where you don't even dream of sending something different. And if they leave you, the rules have to be clear from the beginning - born to improvise on the march, which the messes then come.
Theme laws, of course, you have to look at them. Each country has its move, although, for example, in the European Union it is allowed (Directive 2014/24/EU, in case the regulatory roll), but always meeting certain conditions. It is not to arrive and kiss the saint.
A key point: the variant has to contribute some truth. It is not enough to change four details so that it seems different. If you do not meet the minimum or do not improve the thing, nor bother, that they will throw it away.
Another thing: preparing a variant is usually an extra curro. The evaluation is more tangled than that of the basic offer, so it is convenient to curve it, explain it clearly and justify everything, because if not, they do not look at it.
So, summarizing: Variant offers can be a very good letter for companies that go to public tenders, provided they know the rules of the game and present something that really is worth it. If they do well, they can even surprise the administration and take the cat to the water. But do not skip the rules, that there is no room for the mistake.