It's the new official website for all Epsitec SA games.
Is it really free? Seriously?
Yes, all games can be downloaded freely. It's official and legal. With some games, the source-code is available, see this thread.
You should download in priority the releases provided by this website on top of this page instead of the archives section. The CoLoBoT game is actively developed by the TerranovaTeam. It's no longer maintained by Epsitec SA since 2014. Note that this team own the main repositories for the Buzzing Cars and Blupimania 2 source-codes too. No release are available for these games, then it makes sense to continue to download the archives in this case.
About Planet Blupi, it's a bit different. The official repositories are not really maintained by Epsitec SA, but just by one employee which is working on the games as hobbyist. Nothing new about the game is done under the Epsitec SA name.
Feel free to donate something if you want. The money will be used for paying the hosting, domains and the certificates for example. It's not intended to be used for stuff unrelated to the Blupi games. (For CoLoBoT, Buzzing Cars and Blupimania 2, please look at colobot.info)
Epsitec SA remains the owner of Colobot, CeeBot, BuzzingCars and Blupi names. Daniel Roux is the father of Blupi and all games.