Before Battlefleet Gothic, Games Workshop released Space Fleet in 1991.  It came with 4 plastic ships to build, 2 Imperial and 2 Eldar.  The lid of the box also was used for rolling the dice and was divided into 9 squares and where the dice stopped would determine if the attack hit or not.
GW followed up with articles in multiple White Dwarf magazine issues covering the background of the game a great deal of additional rules and stats and information on the line of metal miniatures that were produced by Citadel.  The articles were in issues 139, 140, 141, 146, 147 of White Dwarf.
The miniatures were quite interesting and the Imperial Fleet grew quite large with many new minis but also some of the support ships were actually re-used miniatures from QT Models whose ships had been aquired by Citadel like several of the miniatures in Citadel's Space Cruisers and C43 and C44 lines.
The Eldar fleet only got 2 ships, the metal version of the Wraithship, plastic ship in the box and a smaller Shadowhunter.
The Tyranid Hive Fleet defined in White Dwarf 146 was quite extensive and did feature several ships that had been part of Citadel's Space Cruiser line in the past.

Imperial Fleet These are the rest of the Imperial ships in Space Fleet with new miniatures plus some from the older Citadel Space Cruiser range.  Some of the new ships with armoured prows started the look that was carried through to Battlefleet Gothic. The main battleships need full broadsides so they use weapon arcs offset by 30 degrees, sometimes called Beta Orientation.  Other than the placement of the arcs there is no difference but it allows ships to have full broadside arcs of 12 o'clock to 6 o'clock either port or starboard. The support ships including the Galaxy Troop Ship, Goliath Factory Ship, and Constellation Targeting Ship have have been included.  The Castillian Shield Ship is a tough fit and the Dictator Battleship with the face and grappling arms is beyond what I want to address.
STALWART class Escort Mass 6 Cost 22/16 Average Hull 2 (1/1) Thrust 2 No FTL 1 Fire Control 1 PDS 1 Class 1 Beam Battery
THUNDERBOLT class Cruiser Mass 42 Cost 143/119 Average Hull 12 (3/3/3/3) Armour 3 points Thrust 4 FTL 2 Fire Controls 2 PDSs Level 1 Screens 2 Class 2 Beam Batteries (2xFP/F/FS) 1 Pulse Torpedo (F)
ANNIHILATOR class Battleship Mass 80 Cost 304/288 Average Hull 24 (6/6/6/6) Thrust 2 FTL 2 Fire Controls 2 PDSs Level 2 Screens Turret - 4 arc (F/P/S)   2 x Class 5 K-Guns
TYRANT class Battleship Mass 100 Cost 360/360 Average Hull 28 (7/7/7/7) Armour 4 points Thrust 2 FTL 3 Fire Controls 4 PDSs Level 2 Screens 2 Class 1 Beam Batteries 4 Class 2 Beam Batteries (2xPBS, 2xSBS,) 2 Class 3 Beam Batteries (PBS, SBS) 1 Class 2 Graser (F)
DOMINATOR class Battleship Mass 100 Cost 350/350 Average Hull 28 (7/7/7/7) Armour 45 points Thrust 2 FTL 3 Fire Controls 4 PDSs Level 2 Screens 2 Class 1 Beam Batteries 4 Class 2 Beam Batteries (2xPBS, 2xSBS,) 1 Nova Cannon (F)
EMPEROR class Capital Ship Mass 142 Cost 510/570 Average Hull 40 (10/10/10/10) Armour 5 points Thrust 2 FTL 4 Fire Controls 1 ADFC 6 PDSs Level 2 Screens 2 Class 1 Beam Batteries 4 Class 2 Beam Batteries (2xPBS, 2xSBS,) 4 Class 3 Beam Batteries (2xPBS, 2xSBS) 1 Class 2 Graser (F)
CONSTELLATION class Targeting Ship Mass 38 Cost 151/127 Average Hull 10 (3/3/2/2) Thrust 2 FTL 1 Fire Control 2 PDS 1 Class 1 Beam Battery 4 Superior Sensors
GALAXY class Troop Ship Mass 76 Cost 183/130 Average Hull 22 (6/6/5/5) Thrust 2 FTL 1 Fire Control 2 PDSs Level 1 Screens 1 Class 2 Beam Battery (all arcs) 28 Mass Troop Space (4x7)
GOLIATH class Factory Ship Mass 157 Cost 317/219 Average Hull 40 (10/10/10/10) Thrust 2 FTL 1 Fire Control 2 PDS 2 Class 1 Beam Batteries 80 Mass Fuel Cargo (8x10)