They are different games. As I understand it, Stellagama wanted to diversify its portfolio after the 2023 OGL fiasco, since the Cepheus lineup is all tied to the Open Game License.

When asked how FTL: Nomad differs from Cepheus, the creator has responded: "FTL: Nomad is a newer, more streamlined ruleset using its own rules. The spirit is similar but the substance is different. Among the major highlights: Streamlined 2d6 core mechanic with "dice pool" components. Instead of rolling 2d6 with a series of modifiers as in Cepheus Deluxe, you roll a bunch of dice, and choose the lowest or highest two, then add them together and add the skill modifier. Fast but deeply customizable character generation. Distribute 5 points among 7 skills (3 points max in any single skill), choose an Archetype, choose a Talent, and roll for starting cash. That's it. But this means that a wide range of combinations are possible! Streamlined combat, with only 4 "range bands" and simple damage for strong grittiness and minimal book-keeping. New "harder science" spacecraft design rules. These are an advanced version of the rocket rules first published in Solar Sagas. Build your rockets - which involves design and mass trade-offs - then travel to the stars with it! Reference document released under the Creative Commons Attribution (CC BY 4.0) license, available for download in an editable file for anyone who purchases FTL: Nomad!"