Theme: Desktop Adjunct - Multifunctional device that goes with a computer.
18A. Dodger pitcher with three 1960s Cy Young Awards : SANDY KOUFAX
31A. Friar from Assisi : FRANCISCAN. Friar Alessandro, the "Singing Monk" of Assisi.
41A. Short exercise dash : WIND SPRINT. Usually sprint to a point and sprint back; repeat.
56A. X-ray imaging technique : FLUOROSCOPY. FDA rap on the subject. LINK
46D. With 57-Down, multifunctional office machine suggested by this puzzle's circles : ALL-IN-. 57D. See 46-Down : ONE. I'm happy with my Brothers.
Argyle here with a debut constructor, I believe. Well done; a touch more difficult than our usual fare but fair none-the-less. The circles weren't necessary to solve it.
Across:
4. Infielder's statistic : ASSIST
10. Mop for a deck : SWAB
14. "The Tell-Tale Heart" author : POE, Edgar Allan.
15. Casual slacks : CHINOS. Out of favor? Chinos vs Khakis
16. __ San Lucas: Baja resort : CABO
17. Frying pan spray : PAM
20. Compare prices : SHOP
22. Classic autos : REOs
23. Very overweight : OBESE
24. Blokes : CHAPS
26. Replacements for flat tires : SPARES
27. Prison sentence shortener : PAROLE
29. Restful resorts : SPAs
33. "Over here!" : "PSST!"
37. Honors with a fancy party : FETES
38. National Gallery architect I.M. __ : PEI
39. Second film in a 2000s horror franchise : SAW II
40. Soviet news source : TASS. Launched December 30, 1902.
43. Charge per day, e.g. : RATE
44. Mall booths : KIOSKS
45. Late-night pioneer Johnny : CARSON
49. Tight spots : BINDS
50. Hilo howdy : ALOHA
51. 50-and-over org. : AARP
53. Sign of sleepiness : YAWN
59. Zodiac lion : LEO
60. "Put up your dukes" duke : FIST. I thought of Bert Lahr first.
61. Cut while shaving : NICKED
62. Faux __: blunder : PAS. "My bad"
63. Middle-earth creatures : ENTs. The good tree people.
64. Diners : EATERS. Never heard it used for the building but for those inside, ok.
65. Cloud locale : SKY
Down:
1. iPhone add-ons : APPs. 21D. Text messaging devices : PHONES
2. Ark captain : NOAH
3. Blue-staters : DEMOCRATS
4. Cooling units, briefly : ACs. Only need them for a few more days in the NorthEast.
5. Wrinkly Chinese dog : SHAR PEI. Aww!
6. Trig ratios : SINES
7. Prefix with European : INDO
8. Versatile beans : SOYS
9. Cluck of reproach : TSK
10. __ diver : SCUBA
11. Communion bread : WAFER
12. Degrade : ABASE
13. They're stacked in moving vans : BOXES
19. "How clumsy of me!" : "OOPS!"
25. Oct. contest whose winner goes to the World Series : ALCS. (American League Championship Series)
26. __ Diego : SAN
27. Dying-out sound : [PFFT!]
28. Region : AREA
29. Heated argument in public, say : SCENE
30. Settled up : PAID
32. Rotating cooking rod : SPIT. What's cooking?
33. Make fun of : PARODY
34. Region including the Matterhorn : SWISS ALPS
35. Kitchen fixture : SINK
36. Little songbirds : TITs
39. Rotate like a top : SPIN but not like a spit.
41. Pale : WAN
42. Ship's captain : SKIPPER
43. Waterfall sound : ROAR
45. Luigi's drink with latte : CAFFĂ
47. Yank out of bed : ROUST
48. Flu season precautions : SHOTS. The next round will be here soon.
49. Penniless : BROKE
51. India's continent : ASIA
52. Bank holding: Abbr. : ACCT.
54. Frail from the flu, say : WEAK
55. Minding business that's not your own : NOSY
58. NFL gains : YDs. (yards)
Argyle