Three tables to roll an alternate Venus (or Venus-like) world for your old-school campaigns.
General Planetary Conditions
1. Dense (crushing) Atmosphere, unbreathable, surface temperatures high enough to melt lead.
2. Dense (crushing) Atmosphere unsurvivable by humans at low altitudes, high altitude contained habitats survivable but oxygen supplement needed to breathe outside habitats.
3. Dense Atmosphere unsurvivable by humans at low altitudes, high altitude jungle environment habitable.
3. CO2 rich atmosphere hot but endurable, filter mask required to breath outside habitats for human.
4. Thick but breathable atmosphere with surface ravaged by toxic clouds that periodically rain insidious acid rain.
5. Oxygen rich atmosphere requires filter masks to breath, frequent vast fires create they cloud deck that blocks out sunlight keeping surface survivable (aside from the frequent fires).
6. Otherwise breathable atmosphere tainted by gases bubbling from the vast seas of rotting biological matter. The seas are a riot of grotesque life-forms in an aggressive Darwinian contest.
7. A Seeming tropical paradise save for the toxic atmosphere which would kill humans in minutes.
8. A steaming world spanning Tropical jungle filled with dinosaurian life.
9. A riot of fungus-like growths dominate the lowlands in such profusion the spores are dangerous to human life. In the uplands isolated communities struggle to keep the infestation at bay.
10. An ocean world wracked by and ever storm filled sky conceals a vibrant and diverse aquatic ecology in the depths of the oceans.
11. A steaming ocean world where the only surface is vast island-mats of vegetations. Great beasts of immense size swim in the seas mostly ignoring the relatively pathetic surface life that clings to the island-mats.
12. A world choked in the gases of a once great technological civilization. Little pockets of life exist isolated in precarious local ecologies but on the main the seas, land, and air are filthy with wastes from the fallen civilization.
Native Intelligent Species (roll 1d3, if more than one choose one to be dominant)
1. Blind Spiked Crustaceans
2. Levitating Cephalapods
3. Sentient Bivalves
4. Tripodal Fungoids
5. Chthonian Horrors
6. Communal Vegetable Intelligence
7. Gargantuan Insects
8. Large Singing Snails
9. Savage Reptilians
10. Sophisticated Myriapods
11. Machines from an elder civilization
12. Forgotten Atlantean Colonists/Amazons
Native Technology (roll 1d12 for dominant culture, 1d8 for others)
1. Non-technological society
2. Primitive/Stone Age; tools shaped directly from raw goods in the environment
3. Pharaonic; Chariot-like vehicles and pyramids
4. Bronze Age; catapults and small ships
5. Medieval; castle, swords, and handwritten books
6. Steam Age; an age of industry and science overtaking older way of life
7. Diesel Age; roughly analogous to the middle of the 20th century
8. Crystal Age; harmonic vibrational weapons and healing crystals
9. Space Age; Orbital weapons, Superalloy
10.Bio-Tech; Cultured materials and bio alteration
11.Psychotronic; Astral Detonators, Psychoactive beat
12.Cosmic; appears to be magi-tech to primitives
Some of the general conditions seem like they would prohibit much in the way of local species being around. Those that do seem out of place could be in isolated habitats (dungeons, domes, towers, redoubts, spaceships), micro-environments, just a notion to describe long lost ruins, or the undead remnants of a previous civilization.
Dense Atmosphere unsurvivable by humans at low altitudes, high altitude jungle environment habitable. Crustaceans and Insectoids with medieval technology battle it out over control of the lowlands while the remnants of an Atlantean colony struggle to survive in isolated mountain citadels with their slowly failing crystalline technology (they are ignorant of the fate of Atlantis on Earth).