When comparing Old School Reference and Indexing Compilation (OSRIC) vs Icar, the Slant community recommends Old School Reference and Indexing Compilation (OSRIC) for most people. In the question“What are the best tabletop RPGs?” Old School Reference and Indexing Compilation (OSRIC) is ranked 32nd while Icar is ranked 52nd. The most important reason people chose Old School Reference and Indexing Compilation (OSRIC) is:
OSRIC is based on the well-known 1st edition of Advanced Dungeons & Dragons, arguably the most popular RPG of all time. It doesn't stick to is slavishly, though, but instead brings in a few innovations from the later "d20 SRD" to regularize the system a bit and fill in some of the gaps. It is, however, still very much a 1980s system.
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Pros
Pro AD&D 1E aligned to d20 SRD
OSRIC is based on the well-known 1st edition of Advanced Dungeons & Dragons, arguably the most popular RPG of all time. It doesn't stick to is slavishly, though, but instead brings in a few innovations from the later "d20 SRD" to regularize the system a bit and fill in some of the gaps. It is, however, still very much a 1980s system.
Pro Super strategic hand to hand combat and piloting rules
Cons
Con Complex and inconsistent rules
There is no "general system" for doing things in the game - everything is a special case. This can result in a lot of page-flipping to find the particular rules for something, and in problems for new GMs who don't yet know the system well, or who aren't comfortable with improvising.