Unreal Tournament is practically one of the forefathers of online shooters. You know sounds like “HEADSHOT!” or “MULTIKILL!” from CS servers? The originals actually come from UT… It's a really funny game, considering how old it actually is.
UT99 is still available at GOG, with alleged compatibility up to Win 10, but not in good old Germany. Because there the game is still on the so-called index. Therefore it is not allowed to advertise the game freely in Germany.
First install from CD/Image. You should install the patch (it's the last one anyway, so you don't have to install another one anyway). The patch can only be installed with a CD (or image) inserted. The game does not need its CD after the installation. So you won't need a crack. However, the game will possibly cause certain problems on current computers, which should (allegedly) be solved with these notes. It has already been reported that the game on Win 7 x64 would not play smoothly on current computers, but also that it works completely without problems.
The UT server of the mobile infantry is, contrary to the standard, accessible via port 7779:
www.mobile-infanterie.de:7779. But at the moment there is the popular multi-core speed stepping problem. When you join, it might stutter endlessly. I haven't found a solution yet on how to handle this. Relevant hints are welcome.
For your own UT server you have to enable ports 7777 and 7778 (UDP). 7777 is necessary for the actual joining, 7778 is for the server data query (map, player and such stuff are queried via it).