Traveller (or T1, by Marc Miller) was the first pen&paper Science Fiction roleplaying game; it came out in 1977. It was followed by MegaTraveller (T2) and Traveller: The New Era (T:NE or T3). After publisher GDW died, Miller restarted with a new company and issued a new Traveller game (T4). There's a GURPS Traveller and a D20 Traveller, too.
I own most of T1, all of T2 and T3, and the basic rules for T4 (was there more to that unfortunate game?).
T2 introduced a very limited XP- and skill upgrading system, but it didn't work too well. T3 finally had a completely new ruleset which made the game compatible with other GDW RPGs (Dark Conspiracy and Twilight/Merc: 2000). There XP and skill boosts played a greater role; they still were measly if compared to XP cornucopiae like AD&D and thus did not exactly have an 'instant reward' effect. IIRC you received one or perhaps two XP per gaming session; you needed many XP to raise a skill, and I don't remember if it was possible to raise attributes at all (it's been more than 10 years since I last GMed one of the GDW games).
There were several (at least two
) MegaTraveller computer games, but to be fair, I never played them.
There were other p&p RPGs without levelling, like Karma and Amber (if I recall correctly).
I consider the Sims an RPG because it has everything I ask of an RPG. Once again, we're at definition level
.