What about the Syrian army?
As news of Assad's departure spread, army soldiers in various parts of the capital Damascus began shedding their military clothes, local residents told AFP.
One eyewitness, requesting anonymity, told AFP they saw dozens of military vehicles abandoned in the upscale Mazzeh district, home to military and security headquarters, embassies and United Nations offices.
The army has not issued an official statement, but soldiers told AFP they were told to leave their positions, with one saying "our direct superior told us to leave and go home, so we knew it was over."
On the highway between the central city of Homs and Damascus, an AFP correspondent saw hundreds of soldiers gathered near rebel checkpoints.
Hundreds of soldiers and rebel fighters have been killed since the offensive began, with fierce battles in the country's north particularly in the first few days.
But government forces withdrew from their positions with no major resistance in some areas, according to the Observatory.
The rebels swiftly took control of several strategic cities within days, starting from second city Aleppo, then central Hama and Homs before marching on the capital.
Thirteen years of civil war have exhausted Syria's military equipment and army, which has lost around half of its personnel, estimated at 300,000 before 2011.
In recent days, analysts have emphasised the military's weakness on the battlefield, without effective Russian or Iranian support.
A source close to Lebanon's Hezbollah told AFP the Iran-backed group had withdrawn from positions in the vicinity of Damascus and in a border area with Lebanon, where it had bases and depots.
Who holds power?
Syrian Prime Minister Mohammed al-Jalali, who took up the post in September, said in a message broadcast on his Facebook page that he was ready to "cooperate" with the leadership chosen by the Syrian people and for any handover procedures.
The rebel factions announced a "new era" in Syria.
The leader of Syrian rebel group Hayat Tahrir al-Sham, Abu Mohammed al-Jolani, ordered forces Sunday not to approach official institutions in Damascus, saying they would remain under the prime minister until they are officially handed over.
In the statement on Telegram, Jolani used his real name Ahmed al-Sharaa instead of his more well-known nom de guerre.
With the army's collapse in areas it controlled, including around critical facilities, the rebels and other armed groups who control swathes of the country face major challenges.
Mohanad Hage Ali from the Carnegie Middle East Center said on X, that "the main challenge today lies in re-building the Syrian state and shifting from the chaos and fragmentation phase."
"Until now, the factions have shown awareness in dealing with minorities and prisoners," he said, amid hope this could help translate "into the reconstruction of state institutions".