8051s pretty much mean Keil - they used to do license dongles, but it's all online now. You really don't get much more established than the 8051. If you pick up any cheap electronic product and crack it open to find a low part count PCB with a black epoxy blob on it, chances are very good there's an 8051 core with a mask ROM under the blob.
(Also AVR/PIC compiler from Microchip had a dongle as recently as February this year, and it looks like it's still available for sale even though its license isn't in the new licensing model).
(Also AVR/PIC compiler from Microchip had a dongle as recently as February this year, and it looks like it's still available for sale even though its license isn't in the new licensing model).