Gunstars, while a successful design, were never built in significant numbers (indeed the total number built never exceeded the amount of Battlestars built), and thus couldn't be everywhere at once. The resources needed to build one of the huge Gunstars were also extravagant, and thus Gunstars never were built quickly.
This, alas, was unacceptable to Colonial Command. They needed ships that could take on Baseships and win (the Gunstars), or ships that when combined with an escort could inflict major damage on a Baseship.

The Libra Class Destroyer was the result. It goes against most Colonial doctrine by not carrying many fighters, but the space freed up by this was used to install large pulsar lasers. Large power plants were installed to power these weapons.

Alas, the Libra Class was not a qualified success, the main reason being its lack of fighters. Most commanders tried initially to use the Destroyer as a cheap-mans Gunstar, and without adequate fighter support, that tactic just amounted to a lost ship, because while the Libra did have the firepower to damage a Baseship, it couldn't really do much against its fighter escort.
Once commanders started realising this, the ship was put to good use. With a couple of CVL escorts and usually a CLE, the Destroyer Squadron (as the grouping of ships was called) was sent in action, usually with some good results. Against lone Baseships these Squadrons had a reasonable chance of destroying it, although usually resulting in the destruction of at least half the squadron itself. Against multiple baseships, squadrons were annihilated.

Still, the Colonials devised ambushes and other sleight of hand tactics, and Destroyer Squadrons became the backbone of the Colonial Fleet and the unsung heroes of the war.

Variants:

There was a few variations to the Destroyer, one was that of the Aquaria Class Destroyer Carrier. It was realised when a Destroyer limped home with major damage to its pulsar lasers, and no replacements were available at that time. Instead of seeing the ship wasted, the damaged lasers were ripped out and additional fighter bays were installed.
With power to spare now that the ship had no heavy weapons, it became one of the fastest ships in the fleet, and was used on strike missions providing fighter and escort protection. Like the Destroyer, it was not an outrageous success. It couldn't carry enough fighters for decisive action, and while the speed was a bonus, it had no heavy weapons to supplement this. Still, a few destroyers were converted to this design, but most of these ended up on escort duty in rear areas.

Another variant was the Leosia Class Missile Destroyer. Owing more to the DDV than the DD itself, the Missile Destroyer again had the pulsar lasers removed and this time replaced with missile racks. It had the speed of the DDV (which was impressive), and had a good hitting potential. It was never built in large numbers as it was deemed a resource intensive ship, requiring constant re-supply for it is missiles after every battle. Still, it did prove to be a capable ship when supported with fighter cover and missile carrying transports. The DDD was actually the saviour of the DDV. Being able to achieve the same speeds, the two types of ship were sometimes (rarely though) combined into 'true' destroyer squadrons. Not a brilliant success, but worth enough to make it more than a one-off.

A final major variant was the Eidolon Class Destroyer Scout. This class of ship had all of its heavy weapons removed and replaced with a large and powerful sensor package - one of the most powerful mounted on any Colonial ship. The large (and generally considered useless) cargo bay was replaced by expanded laboratory space and two additional Asp recon fighters were added. Finally, in an attempt to compensate slightly for the loss of firepower, some additional turbolaser batteries were added to replace the heavier weapons. With the larger weapons prone to blinding and rendering the sensors useless, these smaller weapons were deemed far more suitable. Issued in an attempt to replace light cruisers being employed in Destroyer squadrons, the DDS was a successful design, and when teamed with additional destroyers and a Thera Class medium carrier, destroyer squadrons become more than capable of taking on the best the Cylon Empire had to offer. Unfortunately there were never enough of them to go round, so it was a dream that never fully realised.

Not a specific variant in themselves, some destroyers were outfitted with faster hyperspeed engines enabling them to travel between the stars at a much increased rate. Ships of these types were placed together in 'fast squadrons' and dispatched on raiding missions deep into Cylon space, either taking out critical targets or acting as decoys to lure enemy forces away from other strike missions. Because of their reduced power requirements, the DDV and DDD were usually selected to become Fast Destroyers, which were designated with the suffix -F, thus a DDD Fast Destroyer becomes a DDD-F.

The Destroyer was drawn by Dave Charnow and designed by Dexter Smith and Brandon Bray.
Note that the Destroyer as presented on here, is smaller than the one on the Newsflash site. The SSD's were designed and drawn by me.

Destroyers have one large shuttle bay. The bay has a launch tube ([J1.54] which will propel a fighter flight to speed 12 and will launch in direction 1 and a standard shuttle hatch (launching and landing in direction 4).
The DDV has two shuttle bays, and transfers are possible via (J1.59).
The shuttle bay is large enough to accept yachts.
Destroyers have a hyperspeed multiplier of x1. Fast Destoyers have a multiplier of x0.75. This does not change their BPV.

Colonial Destroyer boarding diagram:

Master Ship Chart Extract:

Annex #7B: Ships able to land on planets

This ship may not land on a planet.

Annex #7G: Carrier information & Annex #7N: Missile reloads