An internet connection. At least at 56k, but you will be laggy, so a much faster (broadband speed) would probably go down better. And thats it for playing standard Freelancer online.

If you want play on some of the modded servers however (and there is quite a few out there), you will also need a copy of Freelancer Mod Manager (FLMM) which can be downloaded from this site, plus which ever mods you wish to play (again, most mods are available from this site and there is a large selection to choose from. Some of the most popular include Total War, Evo, Next Gen and Freeworlds).

Freeworlds Mod Developer
Author of Modular Station

'There is no Good nor Evil in the universe, just perceptions and circumstances.'

Thanks for the info how do you distinguish between mod serves and regular ones

Nine out of ten times it's listed under "server name" like "Boston 24/7 running Epsilon 2.58" or something. At the right, under the "version" column, a server with version 1.00 is clean (without mods).

Please correct me if I'm wrong. Haven't played online in a while

Thats essentially it. Most modded servers have the name in their title and most also change the version number, so you can't access the server anyway without the mod installed (as the mod changes the version number on both your side (client side) and the Server Side). You will not be able to connect to servers which have a different version number to the game you are playing. Standard Freelancer is v1.0, while mods can have a number of wildly different version numbers.

Freeworlds Mod Developer
Author of Modular Station

'There is no Good nor Evil in the universe, just perceptions and circumstances.'