www.sgtools.info

Logging in just gives this site access to reading your profile data. It uses Steam API and there's no risk in using it (sites and apps using Steam API have no power over your account, they're just means to identify yourself).

Yup recently there is a lot of link with sgtools.info link, is this normal?

Yes, it is secure (at least it's not a malicious site, if that's what you were worried about). The goal is... depending on the GA creator. Some want to make GA only for lvl, say 1-3 and you can't make it with SG tools - you could only keep the lvl 0 people but not 4-10 lvl folks. Other and more popular is checking the ratio of wins. Someone can be lvl 1 with 1 giveaway and 100 won games, another person can give 4 games and 4 as well.

I hope my explanation helps :)

It is secure.
The goal is that SGT is outside site of SG, it doesn't have access to your SG session ID, so when you enter it it doesn't know what SG user you are. And as it needs that information to check if you meet GA criteria it uses Steam login data, compare it with SG profile corresponding to your Steam profile and thus is able to check your SG profile for GA criteria and if you meet them give you SG GA link.

As for other uses - you can also use SGTools to check if users have for example not-activated wins, what is their Real Contributor Value, how much exactly they require to level up, check bundled games and so on.

Thanks for the fast answers
Have a nice day (weekend)