Fresno
Chefs credit it with a more complex flavor than the jalapeño, according to Valley Public Radio.
2,500 to 10,000 SHU, per Wikipedia (Fresno chile), uncited there; Valley Public Radio calls it slightly hotter than a jalapeño. Log scale against the hottest chile in this guide.
The Fresno is a fresh, conical chile about two inches long that ripens from green to bright red. Clarence Brown Hamlin released it in 1952 and named it for Fresno County, California. It is a salsa and hot-sauce chile, and it rarely appears in chili.
Valley Public Radio reports that the seed merchant Clarence Brown Hamlin developed the chile at his farm in Clovis and named it for his home county. Wikipedia dates its release to 1952 and says it is grown mainly in the San Joaquin Valley.
The pods are about two inches long and an inch wide at the stem, and ripen from bright green through orange to red. The Fresno is often mistaken for a jalapeño, but Wikipedia notes that it grows point up rather than point down and is genetically distinct.
It is used fresh in salsas and ceviche, and red Fresnos are fermented into hot sauce, as in America’s Test Kitchen’s easy homemade hot sauce. Wikipedia notes that its walls make it a poor chile for drying into powder.