I noticed that Frontier has added several less than dailies this summer, going back to a model from couple of years ago.
Some new routes:
PHL-IND (3x weekly) Sun, Tue, Thurs
PHL-CLE (4x weekly), M W F Sat
PHL-CVG (4x weekly) M W F Sat
PHL-BNA (4x weekly) M W F Sat
PHL-MKE (3x weekly). Sun, Tue, Thurs
PHL-MSY (3x weekly) Sun, Tue, Thurs
PHL-AUS (3x weekly). Sun, Tue, Thurs. Suprised to see this one, as AA even suspended this route for some time because of it's length.

I think this 3-4x weekly model out of PHL should work out somewhat better than from TTN, as atleast pax can fly back on AA if not on F9 if return flight doesn't work out or vice versa. But, it might be still less obvious when F9 is flying the route.

From last year, most of these get restored
CLE-ATL (daily)
PHL-CLT (4x weekly)
PHL-ORD (3x weekly)
TTN-ORD (4x weekly)
IAD-ORD (3x weekly)
PHL-ATL (missing in action, but a bloodbath currently even with F9 bowing out)
TTN-ATL (daily)
TTN-DTW (daily)
TTN-RDU (4x weekly)
TTN-CLT (3x weekly)

Certain routes like PHL-DTW, and PHL-MSP have been added recently by Spirit, and Frontier did not add them back. I'm surprised TTN-MSP wasn't added back.


The DEN hub also is connected well to most of it's stations as well this summer.
CLE-DEN returns, RDU-DEN returns as well, with CLT-DEN, GSO-DEN (4x weekly) and PHL-DEN.

I also see that CLE-IAH is being offered as a nonstop on certain dates. However, Frontier's website also sells a circuitous CLE-DEN-IAH that is showing up making it difficult to see when CLE-IAH actually operates as a nonstop. Frontier's site is even selling a CLE-DEN-CLT, ATL-DEN-DTW which clutters it's site.

There are also some less than dailies out of ATL as well:
ATL-IAH (3x weekly)
ATL-CVG (4x weekly)
ATL-IND (3x weekly)

CLE-LAX is also being sold, at 3 or 4x weekly, along with CLE-SEA at 3 or 4x weekly.

I suspect F9 will rely alot on third party sites to expand visibility for these less than daily offerings, but I suppose most already check kayak to see what's the lowest price offered.