Lego PF Medium Motor with gears and pulleys lifts a hefty 102.2 kg. Gear ratio 15:1 and tackle velocity ratio 8:1. Only lego parts were used, except for the string. Enjoy! :)

Development videos:
Part 1 pulleys: https://www.youtube.com/watch?v=KUjVby8H-bQ
Part 2 gears: https://www.youtube.com/watch?v=umN2iHsw3UY
Part 3 gears and pulleys: https://www.youtube.com/watch?v=slv5fvS6e9Q

List of parts:
1.5 meters of string Stabilit Vielzweckschnur auf Polyamid 1.3 mm, max 25 kg (bought from Bauhaus)
1x Power Functions M-Motor (8883)
1x Power Functions Battery Box (8881)
1x Power Functions Control Switch (8869)
2x Plate 2 x 16 (4282)
2x Plate 2 x 4 (3020)
12x Technic, Brick 1 x 16 with Holes (3703)
2x Technic, Brick 1 x 6 with Holes (3894)
6x Technic, Brick 1 x 4 with Holes (3701)
1x Technic, Liftarm 1 x 2 Thick (43857)
1x Technic, Liftarm 1 x 2 Thin (41677)
2x Technic, Pin 3L with Friction Ridges Lengthwise (6558)
2x Technic, Pin with Friction Ridges Lengthwise WITH Center Slots (2780)
1x Technic, Axle 16 (50451)
2x Technic, Axle 12 (3708)
4x Technic, Axle 6 (3706)
4x Technic, Gear 40 Tooth (3649)
2x Technic, Gear 24 Tooth (3648)
6x Technic, Gear 8 Tooth (3647)
3x Technic Wedge Belt Wheel (Pulley) (4185)
9x Technic Bush (3713)
5x Technic Bush 1/2 Smooth (4265c)

The pulley block parts:
4x Technic, Brick 1 x 8 with Holes (3702)
3x Technic Wedge Belt Wheel (Pulley) (4185)
3x Technic, Axle 8 (3707)
1x Technic, Axle 10 (3737)
8x Technic Bush 1/2 Smooth (4265c)
18x Technic Bush 1/2 Toothed Type I (4265a)

Note to builders: Protect your eyes and fingers! We are dealing with some serious forces here.