FreeSpace 4x
Paying for research. Research is paid in Resources. The Research Allocation on the Economy screen sends that share of your empire's yearly Resources to research, and every Resource your planets' production queues leave unused that year goes to research too. It all flows into the Active Research Field (or the field the Research Queue picks). With the Generalized Research trait half goes to the current field and 15% to each of the six fields.
Levels and costs. Each of the six fields runs from level 0 to 26. When a field collects enough Resources it gains a level, and any extra carries over. Level costs grow quickly (50, 80, 130, 210, 340, 550 and so on), and every level costs 10 Resources more for each level you already hold in all six fields together, so research gets dearer as your empire advances. Slower Tech Advances doubles all costs, and a custom race can pay 75% extra or 50% less in chosen fields. The numbers above always show your real cost.
What levels give you. New levels unlock parts, hulls and installations: Energy for shields and power, Weapons for beams, torpedoes and bombs, Propulsion for engines, stargates and mass drivers, Construction for hulls and armor, Electronics for scanners, computers and cloaks, Biotechnology for terraforming and planetary scanners. Levels above an item's requirement also make it cheaper to build (miniaturization). Surviving a battle against ships with better technology gives up to a 50% chance to learn a level in a field where the enemy was ahead.
Technology Tree. Pick one of the six field cards to see its levels in four tiers, Early to Ultimate. Green levels are reached and the gold one is next. Click a level to see what it unlocks; ??? marks technology you have not discovered yet. Research this now makes the shown field the active one.
Research Queue. Plan up to 100 years ahead: add fields for a number of years, or until they reach a level (those entries do not count toward the 100). While the queue runs it chooses the field each year; when a field maxes out early it moves on, and when the queue ends the last field carries on.