From publisher's site web page:
What's O.L.D. is N.E.W. is a line of three gorgeous, crunchy, compatible roleplaying games - medieval fantasy, 80s action heroes, and far-future science fiction. These games are called O.L.D., N.O.W., and N.E.W., respectively and are all open (as in open gaming content) and entirely compatible with each other.
Elven musketeers line up in the rain to defend against an oncoming goblin horde. Weathered watchmen investigate a murder in a scummy tavern. Diabolists meddle with things that they shouldn't as they summon the most evil of beings from the depths of Hell. Pirates and swashbucklers battle for supremacy on the high seas. A heroic adventurer adds a moat to his ever-expanding castle.
Bounty hunters track down outlaws hiding in trader towns on worlds at the fringe of the galaxy. Starships explore unknown worlds, going where nobody has gone before. Great generational arks seek somewhere to call home. Detectives investigate a murder in a far-future solar system on a trail which will take them from Mars to Jupiter's moons. Agents infiltrate a criminal organization, going undercover to take down a galactic crime boss. A group of smugglers locate a new hyperdrive system to increase the speed of their freighter.
All three games are rules-crunchy tactical roleplaying games.
None of these games have a default setting (although both will be supported with settings and adventures). They're roleplaying games which encourage you to create your own setting, whether that be a medieval fantasy or far-future sci-fi one. Both games have extensive tools to help you do exactly that, and also to help you tweak dials of low-high fantasy, hard-soft sci-fi, and so on.
O.L.D., N.O.W., and N.E.W. use the same system. Each book is different, however, containing different careers/traditions, equipment, races/species, monsters, and so on. Additionally each has chapters useful to it - O.L.D. has a magic system, herbalism and alchemy, stronghold building rules, a chapter on warfare, wilderness travel; N.E.W. has comprehensive starship construction rules, space combat, cybernetics, and N.O.W. has rules for supervehicles and martial arts.