(source: I'm a son of a retired NMBS worker AND I work in Alstom, so some of this information is first-hand. A little bit is from Wikipedia, so please be careful.)

• MS75/AM75 - built in the years 1975-1977 by La Brugeoise et Nivelles; also nicknamed "Varkensneus" due to its shape. Rarely in service, mostly for international connections to the Netherlands (from Antwerp). Contains ADx + B + B + Bx cars. It can reach a maximum speed of 140 km/h. It's planned to get out of service in 2033.
• MS80/AM80 - built in the years 1980-1983 by La Brugeoise et Nivelles (currently Alstom); two-part units contain ABDx + Bx cars, three-part units contain ABDx + B + Bx (A is 1st class, B is 2nd class, x indicates that it's a motor vehicle). It can reach a maximum speed of 160 km/h. Planned to get out of service in 2034.
• MS86/AM86 - built in the years 1986-1991 by La Brugeoise et Nivelles (currently Alstom) and ACEC; nicknamed "duikbril" due to its distinctive shape. Contains ABDx + (A)Bx cars. It can reach a maximum speed of 120 km/h. Planned to get out of service in 2033.
• MS96/AM96 - also known as DMT, built in the year 1996 by Bombardier Transportation (previously La Brugeoise et Nivelles, now Alstom). Nicknamed "Deense Neus" or "platte neus". Contains Bx + B + ADx cars. It can reach a maximum speed of 160 km/h.
• I11 - almost identical to the MS96, but it has the destination screen on each car and the MS96 trains have a current collector on the middle car. Built in the years 1995-1997 by Bombardier Transportation. They contain A, B and BDX cars. It can reach a maximum speed of 200 km/h.
• MR08/AM08 - built in the years 2009-2015 by Siemens Mobility and Bombardier Transportation; it belongs to the Desiro family, so it's in fact a light train. Contains ABx + B + ABDx cars and can reach a maximum speed of 160 km/h. It has a distinctive acceleration sound.
• M5 - the first double-deck train, built in the year 1986-1987 by Bombardier Transportation. Contains of AB (1st class on the top floor, 2nd class on the bottom floor), B (the whole 2nd class) and BDx (multifunctional car with places for bikes anf wheelchairs, which is also a control car). It can reach a maximum speed of 140 km/h. It's planned to get out of service in 2033.
• M6 - the second double-deck train, built in the years 1999 - 2011 by Bombardier Transportation and Alstom. They contain type A (1st class), B (2nd class), (A)BD (multifunctional cars with places for bikes and wheelchairs) and Bx (control cars). They can reach a maximum speed of 160 km/h, but it's part adjusted to 200 km/h.
• M7 - the third double-deck train, built in the years 2015 - now, by Bombardier Transportation (currently Alstom). It contains the AB (1st class on the top floor, 2nd class on the bottom floor), B (the whole 2nd class), BD (multifunctional cars with 8 places for bikes or wheelchairs, 2nd class - started manufacturing in 2024), BDx (multifunctional control cars with 12 places for bikes and wheelchairs), BVx (multifunctional control cars with 16 places exclusively for bikes - started manufacturing in 2023) and Bmx (motor cars with no space for bikes or wheelchairs, less seats than BDx and a current collector on the roof, also compatible with M5 and M6 trains). It can reach a maximum speed of 200 km/h.