We are going to add support for Linux and Mac as soon as possible, unfortunately I cannot provide an ETA for now.
Do you mean “Manual Groups” from UVPM 2? Manual grouping was in fact significantly improved in UVPM 3 - you can now create a grouping scheme with a set of named groups and assign UVs to the groups in a similar manner as in UVPM 2. You can also export such a grouping scheme to an external file, so you can easily import the scheme in a different blend file.
For more info on grouping schemes, refer to this page in the documentation.