Fflecsi (stylised fflecsi; Welsh pronunciation: [flɛksi]) is a trial demand-responsive bus service administered by Transport for Wales (TfW) and local authorities, operated by local bus operators across Wales. Pilot trials of the service are conducted across Wales, which included a city-wide trial in Newport until September 2022. The effectiveness of the service is being monitored as full bus services resume in Wales during the COVID-19 pandemic. During the pilots, fflecsi will replace some pre-existing scheduled bus routes in the service areas where it operates. The technology behind the service is made by ViaVan, and the pilot is funded by the Welsh Government, to invest in new approaches to public transport in Wales as part of their Llwybr Newydd strategy. The pilot was included in Welsh Labour's manifesto for the 2021 Senedd election, as part of their plan to increase investment in bus services, and reducing Wales' carbon emissions.

Passengers book and pay for journeys via an app (or telephone call), which then matches passengers travelling between similar points, calculating an ad hoc route to the destinations required within the route's service area. Most routes have a fixed start and end destination. The on-demand bus service scheme is charged with normal bus fares, with provisions for seasonal and pre-purchased tickets, MyTravelpass, and 60+ or disabled concessionary travel card. Payments are taken using either a contactless card or Smartcard, although some services may accept cash payments.

By the beginning of September 2020, fflecsi had recorded over 7,000 journeys on its service since its launch in mid-May 2020, according to the Welsh Government. In September 2020, up to 48% of all journeys were from the Newport service as being the only one at the time primarily operating in a city centre. The Newport pilot service ended on 25 September 2022. Services in rural areas were shown to increase passenger demand when compared to the previous fixed bus operations. From May 2020 to May 2021, it had recorded 50,000 trips on its then seven pilot services across Wales, with four being single bus routes.

Fflecsi was first introduced in Newport on 18 May 2020 in co-operation with Newport Transport (Newport Bus). The following day, a briefing was hosted to introduce the concept to Pembrokeshire, another area where fflecsi aims to operate.

On 25 June 2020, it was announced that NAT Group (New Adventure Travel), in partnership with Cardiff Council and TfW, would launch a DRT service for the fflecsi G1 route, replacing the pre-existing G1 NAT Group route, between Gabalfa and Gwaelod-y-Garth via Whitchurch. The service commenced on 29 June, and operated as a trial for three months.

On 20 July 2020, fflecsi started operating in Rhondda Cynon Taf, taking over the 152 route in partnership with Stagecoach (previous sole-operator of the 152 route) and the local council. The route is from Tonypandy and Hendreforgan, stopping in destinations in the communities of Penygraig, Williamstown, Penrhiwfer, Tonyrefail and Thomastown.

On 3 August 2020, the trial service started operating in north Wales. Fflecsi was rolled out in Denbigh and Prestatyn, in co-operation with Denbighshire County Council and local bus operators.

In late August 2020, Newport Bus announced that the 26/26A route to St Julians would be discontinued on 1 September, however, they later reversed the decision and announced that area 1 services will continue. Although reports of stranded passengers followed as confusion over the reinstatement still lingered, with drivers saying their services didn't serve the areas some passengers booked for, whilst the app allowed such bookings.